Eliminating spade connectors, upgrading bits, soldering all of it in

@decooney 
Congrats on taking this bold step to improving the sound of your system.

We've been doing this for decades.  I'm still stunned at times by the sonic improvements as a result of just "getting things out of the way that make it sound worse." Yes, you get the expected improvements in focus and detail.  But, the shocker (at least to me) is the sonic character changes for the better.  In other words, the tonality, balance, chord structures, etc are vastly improved resulting it a much more satisfying (and listenable) musical experience.

@gdaddy1 Good point about heat to those tinder tinsel leads, voice coils, ribbons, etc. Frankly, I hadn't thought of that.  Thanks for bringing it up.  I would like to add that when "stuff" is in the way, it has a tendency to introduce dynamic compression.  Also, the extra "slop" and "muddiness" makes signals stick around longer than they should.  Increasing dynamic range often results in the listener nudging the volume back a tad because a satisfying sound level is happening due to the fact that you're improving the dynamic headroom of the signal.  Improved (faster) transients present the signal for a shorter period of time to the driver (and tinsel leads) thus delivering less average power over a period of time.  Less chance of breaking something.

As mentioned spades/lugs are efficient in the manufacturing process.  But, they do offer one additional benefit for the manufacturer -- ease of in field service if required.  It does not take a tech (with soldering skills)  to pull a component in the field, and the manufacturer can often instruct the dealer (even the end user in some cases) to pull the component and ship it back to them for replacement.

And, finally, @gdaddy1 stated "Yes and it's not just one connection, it's lots of them."

As a race car designer once said:

"If you want to shave 100 pounds off a race car, you have to find 1,600 ways to save an ounce."

@waytoomuchstuff 

The first time I went to solder to the speaker tab I found the thickness of the metal required a higher/longer heat time in order to get the solder to properly 'flow' onto the tab.

I actually saw the effect of the heat run down the little tinsel lead. I think those little leads are coated with a varnish as a protective coating to prevent oxidation to the copper. As it heated up the color changed and it actually smoked a tiny bit. Yikes!

It requires a hot iron, a little flux on the tab and plenty of heat sink 'Play-Doh' on the tabs lower portion. After the joint is made you'll find the play-dough is completely dry and crumbly. It falls off easily. It absorbed all the heat perfectly and the tinsel remains unmolested.

If not done correctly there can be more harm than good.

Other than purely sonic benifits there is the point of durability and reliability. The solder joint with outperform over time. Mechanical connections can loosen due to vibration, thermal cycling, or oxidation, increasing resistance or causing intermittent failures. Soldered joints are far less prone to these issues, ensuring consistent performance over decades.

Good luck!

I just can't imagine doing something like this.  The amount of heat it takes for a proper solder joint for large gauge cable could totally destroy a circuit board!  

Then there is the issue of audio signals trudging through an amalgam of metals including lead vs a proper crimp joint of a pure metal conductor.  

Lastly,  you effectively destroy the resale value of that gear.

It may sound different, but for the above reasons I would never go down that road. 

Now, using a better connector---sure!

I am all for replacing cheap binding posts with good quality copper or copper alloy posts. But the notion of solder being a superior connection is rather perplexing. A crimp or screw connection can be equally gas-tight if done correctly. 
 

When soldering you want to be sure to have a good mechanical connection between the wire and solder tab prior to applying the solder, otherwise the connection is compromised and really no better than a push-on spade. 

And certainly, you will definitely hear an improvement if you remotely expect one, even if that expectation lies way down in your subconscious. 
 

At issue with  connectors is connector quality and metallurgy. OEM often choose cost over quality, and then we have all these interactions with various metals coming into contact with one another. All my line, phono preamps and SET and push pull tube amps point to point wired, no more circuit boards in these components for me. I also don't solder every connection, don't like crimps but have some clamping connectors. Paying great attention to wire quality, connections, especially in signal path is as important as the caps, resistors, etc to me. The boutique parts manufacturers also find metallurgy to be critical in voicing of their products.