A butt-load spent in cables - how much improvemt?

Bring your speakers out more. You have the space. I'm certain they can match the room acoustics much better if you experiment a little.
Also, this is a VERY inexpensive tweak.
As to cables, my feeling is Home Depot extentsion cord can sound as good as $1000 speaker cables. I have experienced it myself. Sometimes the expensive stuff merely sounds different, not better. There was a A/B comparison done by Absolute Sound a fre years ago and HD extension cord was near the top with multi-thousand cables. No kidding.
Please do compare and post your results.
Good Luck.

You never need apologize for conducting your own back-to-back tests of what works best for you. If you put the old cables back and are pleased with the results, you can re-sell your expensive cables and save a bunch of money. If you find the expensive ones sound better, you can give yourself some peace that your money was well-spent.

While hardly unique to high-end audio, we can apply enormous psychological pressure to ourselves to conform to others' expectations. Heaven forbid that we not be sophisticated enough as trained listeners to not hear "obvious" differences! People we don't know might whisper behind our backs about our being country bumpkins or such.

It is very difficult for us to separate advertising hype, fads and fashions from what we really hear. However, I wish more people would do what you've proposed. Haul out the old stuff and do a reality check - compare it to the new. Then choose the one that makes sense to you.

Note that none of this requires you denigrate the one you don't pick. You are not writing your thesis for your PhD, nor are you declaring what is good and noble for the world at large. You're simply choosing some wire for your stereo.

I have found that it is much easier to hear a downgrade in performance rather than an upgrade. When doing cables, this is particularly easy, rather than having to switch out a big component. The "wow" factor is really evident on the downgrade, so swapping around should give you a definite answer!

Has anyone else noticed this phenomenon?

I would not want to be forced to do a blind test.

I've spent to much on cables. Of all I've owned I like the Monster Sigma retro the best. I've tried a few expensive brands (will not mention the names). I've also heard cables that cost 6-7 times what the retros cost at retail. The guy who had me listen to these cables insisted they made a hugh difference. I heard nothing. If I had it to do over again I would probably stay away from the expensive cable game. It is amazing to me the claims made by people about cables. Keep in mind folks, many times people hear all this extra detail due to cables. This is after the very music they are listening to went through hundreds of feet of the cheapest cables available at the studio or concert venue. Cables that are being walked on and not properly cared for at all.

That being said, if you can truly afford it - go for it. My feelings about the cable game are the same as vman71. That is do they do anything at all. When I am being 100% honest, I honestly can't give you a definitive answer. I can tell you for the last 2 years when I need a cable I go directly to Frank at signal cable. I have not been disappointed yet. I also don't sit and wonder how much better my system would be if I spent $20,000.00 on cables. I've heard a system that had that kind of money tied up in the cables. All I could think while I was listening was this should sound better. I thought this because it did not sound any better than mine. We had the same amplifier and the same phono cartridge.

Fatparrot,
I also hear a marked difference when downgrading the cables,components. Maybe because the new stuff usually has to go through a lengthy break-in period before you notice the improvement. The older cables need basically a short "settling" in period, so the ear has less time to adapt.