WOULD IT BE DUMB TO BUY A MARK LEVINSON NO 23.5

I'll second comments that its a bit sterile sounding, but i'll also second comments that its well made.  And while electrolytic capacitors degrade with age - my experience, having shipped -- and seen the results -- 100s of units is that if you really use top quality parts, and run them well within limits, the problems begin 30 years out - not 15.  Yea, i had some cap failures but in retrospect the problem was usually a modest oversight on my part. Ive frankly had more problems with new Chinese capacitors than with old US and European made ones. Or the quality Japanese brands.  Caveat emptor w/r/t specs.

Now, on to re-capping without schematics.  remove cap. Look at specs.  replace cap.  Who needs a schematic?  yes, they are nice to have to identify critical components - but we're talking preventative replacement of things that go boom - not subtle circuit tweeks.
I'll leave the sonic value judgement to the only one who matters.  You.

@testpilot
Yes, taking anything apart can be a pain. Try real consumer gear, made to NOT be fixable....
But I would not have expected them to obscure parts values, unless its a very unusual, secret way of using a part. But cap voltages? really? That also means they are buying custom runs - which simply drives up cost on parts that one ought to be able to get from distributor stock.

I had a JC-1 and some later stuff that was clear as day. But that, admittedly, is ancient history.
Anyway, if they are, its a good point.
I'd just measure the DC values and work backwards though.  they can't obscure those!