I own the below system and I am looking for an improvement by upgrading one of the components (budget $2000-3000).

-Graham Audio LS5/8 (large BBC studio monitor speakers)
-Analysis Plus Oval 9 speaker cables
-Mark Levinson ML 23.5 power amp (completely recapped by Madrigal technician)
-Audio Research LS 5 MKII preamp (restored and new tubes)
-VPI Prime turntable with -Dynavector 20x2 H cartridge
-Parasound JC3+ phonostage

Quite standard power cords and interconnects, no power conditioner.

What change would make a significant difference? Larger soundstage, more liquid, open sound without loosing the dynamic punch?

Thank you for your time and I would appreciate any ideas.
You have gotten alot of different opinions but this is where I would start.  First play with the placement of your speakers.  Sometimes if you find the perfect spot in your room the soundstage will open up and your speakers will deliver what you are looking for.  Next I would look at the platform you have your turntable on.  I have a top notch table but it really improved with a 3" maple platform underneath it.  Cost about $300.

Look at a $1,500 - $2,000 lomc.  That along with better vibration management of your VPI will maximize your front end and possibly astonish you.  

I know nothing about your cables but the attention to your source is where I would start.  

My experience was jaw dropping when I added a high quality platform system for my turntable.  The definition of bass, particularly on musical passages that had repetitive kick-drum beats, was a revelation.  Anything with impact became so much more well defined and audible.  My soundstage and imaging was always very good.  But with the new platform system it all became even wider and deeper.  I chose the Symposium Acoustics Segue ISO Platform combined with the Rollerblock Jr. and the upgraded balls of tungsten carbide.  While that type of upgrade may not be what you are seeking at this moment, trust, at some point if you make that upgrade to your system you will be amazed at the experience and very happy with the investment.  By that time I had already made numerous cable upgrades for signal and AC.  Each and every one of those upgrades made a difference so I do recommend doing so.  Adding the Segue ISO with the RBJRs was like having made an entirely new component upgrade to the system, and for a fraction of the price.  Retail is $550 to $650 for that setup, depending on which size of platform that your turntable would require.

Enjoy the fun.
Dear @bms72 : Try the Analysis Plus Silver Oval speaker and IC cables, those are the ones I'm using in my system.

I owned your 23.5 and even today very good amp and competitive with today designs.

The unipivoth VPI change advise is a must to do it due that all unipivots tonearm designs are way unstable and develops higher levels of distortions and can't fulfill the cartridge needs, you need a gimball/fix bearing tonearm design and when you do it you will attest the wide differences for the better against your unipivot with your Dynavector cartridge.
Latter on you can change your HO Dyna for a LOMC Dyna model, your phono stage has enough clean gain to do it.

Regards and enjoy the MUSIC NOT DISTORTIONS,