Cost Effective System Improvement?

My hobby is to get the best possible sound IMO at the lowest possible cost. My system:

Tekton Electron Speakers - Upgraded
Doge 10 Tube Amplifier (generally 30WPC in Class A) with Psvane KT88-TII, GE 5751 3 mica black plate preamp tubes, and NOS Mullard CV4024 phase inverters.
Denafrips Pontus DAC
Canare 4S11 Speaker Cables

I listen only to TIDAL Premium through Bluesound Node 2i using the BluOS on an android tablet. I often listen to vocals and use the following as test tracks:

Vaya Con dios “Don’t Cry for Louie”
Dave’s True Story “Chasin’ The White Line Down”
Dead Can Dance “The Wind That Shakes the Barley”
Harry Nilsson “Without You”
Glen Campbell “By The Time I get To Phoenix”

I would like recommendations on what I might do for a cost effective improvement. I would consider spending $2-4K for different speakers or amplifier. The speakers and/or amplifier would have to weigh less than 80lbs. My back is 75 years old.

I appreciate your recommendations.
A cost effective improvement would be implementing some room/speaker/system set-up and optimization tips offered by Jim Smith in "Get Better Sound". $37.70 plus tax and shipping.

You may discover you don’t need to spend anything on new equipment or loudspeakers.

What I been doing for years. First thing you always need to know is what do you want to improve, what do you want to make better? If you are real happy with the way things sound now and just want "more of everything" that is very different than if you are unhappy because something is off. Lumpy bass, hyped highs, whatever. These are a different story.   

If there is something obvious you can put your finger on then that will be your best shot to cost-effectively upgrade. But if not, then almost always it is much better to leave the components alone and work on making everything perform better.   

This is first and foremost tweaking speaker positioning. Next locate the components and route the wires to avoid interference. Simply straightening out a tangle of wires with everything routed to be at least a couple inches apart, never running parallel or in loops, and when they do come close doing it at right angles, these things are free and do improve sound. Get everything up off the floor while you are at it. Sometimes depending on how bad it was and how good you improve this could be worth a lot.   

Next, get every single component up off the floor, rack, etc. Get Nobsound springs, use them under everything. By this point your system sounds a LOT better but you have spent peanuts so if your money is burning a hole in your pocket consider putting the Electrons on Townshend Podiums. Read the reviews and comments, this will be like a whole system upgrade. Better than a lot of components you could buy.  

OR another terrific move would be a Raven Blackhawk. Or Nighthawk, more in your budget. Either one, huge improvement! I have the Blackhawk, absolutely terrific amp, not too heavy. Put it on Nobsound, or Pods if you really want to impress yourself.  

If you do go Raven, call Dave Thompson and he will recommend tubes specifically for your speakers and taste in music. Seriously, the guy is that good. I am not big into tube rolling, it has been a crapshoot for me over the years. Not so with Dave. The man knows his tubes. Some do cost more but compared to other stuff that is out there his seem a bargain to me.
50% of your sound is the room, room treatment and speaker placement..

Figuring out how to do it, spent the 37.70 like tvad said..

Best dollar spent for a sound return. :-)

Vibration control and decoupling is # 1 for bass management and cleaning up bass bloat and smear.. I always though people did the room first and decoupled their speakers. Then I started posting here and found out a few do it just backwards.

Spikes, bare walls, bare floors and ceilings, Yikes!!

Gear swaps? Not so much for me..

The room first
Clean up the electrical/protect your gear

Everything else.. LOL

$500 worth of RasPi will blow out that BluNode.
So much for "bang for buck."
You get a lot more SQ for a little work.

Ditto on $$ best spent on the room.
I suggest, decouple speakers from the floor, first. It can be like getting a new set of speakers. Herbies, or Sorbothane pads would be the most cost effective way of doing this.
i concur with millercarbon for using springs and with oldhvymec for acoustic cardinal importance...
Consider upgrading your power cables. 
The best, most effective and probably cheapest upgrade is to improve the acoustics of your room.  A dozen or so 5' to 6' artificial Ficus trees scattered around the room will improve the sound more than new equipment.  There are easy to find at discount home dec stores.
If you really are serious about squeezing out the absolute max per dollar, this will be a lot of work, but I highly recommend studying mahgister. Where most of the work comes in, a lot of what he does will look to be honest rather kooky. But this is where you have to really study and learn your stuff. For example, what looks like empty old gas cans with soda straws coming out are helmholtz resonators. A helmholtz resonator is really any container (volume) of air with a restrictive passage leading in and out. Air pressure in the room flows through the passage into the container and back out again, losing energy in the process. The volume inside, together with the diameter and length of the passage, determines the frequency of sound that is most efficiently absorbed.   

Most people just buy these things and so never do understand what is going on. The design can be worked out mathematically, but then you have to know what frequency you want to tune, and work through the math. Or you can do the whole thing by ear, or start with a ballpark math estimate and fine tune by ear. Or use existing product designs as a starting point and creatively build and tune your own.  

This is just one example. His room and posts are chock full of them. Like I said, a lot of work. But for someone with plenty of time and willing to do the work I think you will be surprised how far these kinds of things can take you.
You're done! That's it! From this point it's all diminishing returns.  ;)
Thanks millercarcon but most people dont own an audio dedicated room...And my system is impossible to live with it and a wife in a living room...

I created it to prove to myself i could reach near the highest Hi-Fi to my satisfaction with basic good choosen gear yes, but embeddings controls at NO COST or very low without buying nothing by recreating some basic ideas or some costly devices...

Most people are better to be inspired by what you have which is Hi-FI, more beautiful...And more costly... Though...

 Anyway the truth is simple:  WE embed everything before ANY upgrade....

You’re done! That’s it! From this point it’s all diminishing returns. ;)
No you are right someone could always pay more to buy some difference....

This is somewhat true...

The half truth in your claim is that you dont say the essential: half of S.Q. comes from electrical,mechanical and Especially acoustical controls and treatment...At possibly low cost...Most of the times more than the upgrades you love so much....

Plugging new gear in a wall and putting ready made panels on a wall is not audiophile experience and reviewing them is of no use save to sell one....

Myself i sell common sense at no cost.... Try to beat me...Call me a fool...You could not have any other argument anyway....Save the common place fact that higher end engineering may cost a fortune and be "better"....For sure they are better.....

Acoustic, mechanical control, and even electrical noise floor control could cost low money though and are 50% of the S.Q....( The % is a metaphor and change in function of the relation of the gear with his embeddings controls or lack of)

The question is not, save for a fool, which is the better system in the world, but how can i create a very good satisfying one at lower cost....

But common sense is something that is harder to sell.... For sure.....

By the way you seems to not understand the law of diminushing returns at all.... Ask me and i will explain it to you....I dont joke here... You dont have a clue it seems by the unilateral  way you use it....
Talk with Alvin at Vinshine and ask him if the Hermes or Iris DDC will make a significant difference to your Pontus.  I was surprised at how big the improvement was using the Iris with my Topping D70.

If you are streaming to the BlueSound over bluetooth you can probably get a noticeable improvement by using Roon and streaming to the Bluesound over USB or Ethernet from a dedicated server or PC. 

Upgraded power cords can make a surprisingly large difference in your system. I don't think Audiogon permits me to post links but if you google Aliexpress  Store No. 625558 and then search that Audio Accessory store for  High Quality Nordost odin 7N silver plated Supreme Reference Power Cable you should find some relatively cheap power cords that made an audible difference in my system.  Put them on your amp and your DAC if you want to splurge.

All of that should be around the lower end of your budget.
Component wise, on your front end you have a great DAC, so I’d either upgrade the Bluesound with a good LPS or ditch it all together. I recently moved from a Node2i to a Aurender and it was quite a noticeable improvement. 
Agree 100% with mahgister and millercarbon.  Same result from two different approaches.  All roads may lead to Rome, none will look the same.  It is about the music.
I have the Bluesound Node 2i. I love it, but I do have it connected to an external DAC. That is the fastest way to better sound quality. My advice: Get a better streamer or connect the Bluesound to a better DAC.
what mostly everyone said- optimize your components and room first.

Subsequently, if you still want a sonic uptick, it would help if you told us what is unsatisfactory (e.g. not enough bass, highs to shrill,…) and/or where you want to go (e.g. more bass, warmer midrange,…) and/or if you want to identify/update weakest links.

Ha, just learned that “e.g.” means “example”, I’ve been mistakenly using “i.e.” which means “that is”. You can teach an old man new tricks.
I keep trying Rasberry Pi solutions, they are getting more complex and expense but not any better. Everyone sounds dull, everyone is a nightmare to set up, everyone has been so unreliable I have given it away.
Hard wire your Bluesound, ie or eg, ethernet. Don't use bluetooth. Use an external DAC and bypass the one built in. I use my Parasound's built in DAC which is very good. Use SPDIF. 
Replace NOS Mullard CV4024 phase inverters with GEC A2900 or Brimar 6060 Yellow T for a warm, walk-through midband, or, if you prefer a more transparent neutral sound, Telefunken ECC801S.
You listen to “only” tidal. I would start with your wi-fi connection. First thing I would do is run cat-7 hard wire and drop the wireless. Then look at Small Green Computer company and their products to bring in fiber to the signal path. When I did these upgrades for Quobuz it was night and day improvement. This will also leave you money for room treatments.
Sometimes, not always, speaker cables can make a huge difference.  I have been on both sides of this and can say from first-hand experience, Belden/Canare work absolutely fine and sometimes they can suck depending on your amp/speaker interface. I would not overlook trying out a good pair of cables.  If you're back is bad, I suggest Audience AU24s, which are excellent and easy to work with.  Hopefully your runs are not too long because it can get pricey. Audience cables are often available on the used market at reasonable prices.  I would say any generation of the AU24s are very good. 
+1 for Townshend Podiums best improvement ever for speakers.
One simple upgrade, to my ears at least, would be ditching Tidal for Qobuz.

+1 ditching Tidal for Qobuz
mglik- +1 for Townshend Podiums best improvement ever for speakers. 

Yeah it is hard to believe something so expensive can also be so cost effective. But it is.
Thank you all for your recommendations.

I have already treated the room with acoustic panels. I will work on this more after I move to a different house in March.

I will start off by cleaning up my cables as suggested.

In addition, I will probably go ahead and get an optical Rendu.

I have already orders a couple of sets of Nobsound springs and I expect I will eventually get the Townshend Podiums.

I may also try one of the Raven amplifiers as suggest by but I’m not sure about this. If I return it it will only cost around $270 plus shipping so that not too bad.
My "Cost Effective System Improvement" is totally without cost, but only to those who are regular wearers of eyeglasses.  If you fall into this category, try this -------.   Sit in your "sweet spot" and listen to your favorite music with your eyes closed.   Midway in the piece, remove your glasses and hear the difference !   It always amazed me that audiophiles, who are conscious of every reflective surface in their listening room and spend thousands to adjust and regulate room acoustics, would wear a pair of "reflectors" only inches from their "receptors" !   Try it !  It's free, cost effective and a really big improvement !
   Both Sennheiser and Neumann have developed head-shaped binaural microphones and neither of them come with an eyeglasses option !  I'm just sayin' !
I thought vibration control was some kind of woo-woo thing sold for crazy money to gullible audiophiles. I spent about $400 on a used collection of Black Diamond Racing cones, Round Things and Those Things. I was really questioning my judgment when I received and opened the box. I started out by putting some of them under my tube DAC and KT-88 tube amp. The improvement was the equivalent of $3,000+ in equipment upgrades. Clarity, focus, detail—all the words I see around here—were much improved. I’ve still got a handful left with which to experiment. Thanks to @millercarbon for the BDR tip. So, as others have recommended above, definitely contemplate vibration control.
Acoustics are inextricably part of the sound you hear. You have some acoustic panels but are there enough or too many? Are they in the right place? What about the biggest issue in all rooms: the bass?

Get a free download like HolmImpulse or REW and a microphone and remove the guesswork. Once you start understanding, and it's not difficult, it becomes a lot of fun and will reward you more than anything else. Appreciate that when the room is sorted out you will better hear any tweaks you try.

Another bit of advice is to ignore the suggestion to fill your room with imitation ficus trees. At best they may serve as narrow-band diffusers.  A measurement system would clearly show that the ficus trees are not helping with the room problem which is the sound taking too long to decay. A bunch of dust collecting ficus trees to solve these problems is simply ridiculous.