I feel that it’s about: Pleasant sounds, pleasant appearance, price/performance. The first two are highly subjective in that I like scalpel-sharp accuracy above pleasant harmonics and reflections, I like several types of faceplate between silver, black, and glass. The final point being price/performance is reliant partially on the other two. None of this matters to the next guy because he might like exposed tubes, gold faceplates, the smell of warm circuits, pleasant harmonics, echos in the room, ...
If you want the huge silver face of (for example) an SX-1980, I don’t see the price/performance ratio ever tipping in your favor as its value is as a collectible TOTL receiver for that marque for that era. OTOH my son prefers some of the higher-performance Pioneer Elite series for far less money, ...
If you like the symmetrical look and thumbwheel tuning of marantz, pretty much all of this gear has a very high price/performance ratio in the specification world, but if you are instead a fan of their “house sound” then they perform better than anything else, and look great. Sansui made some great looking gear, and if you like black faceplates IMO they made some of the best stuff, and the specs were pretty impressive also.
OTOH if you just want a great vintage sound and silver faceplate, other quality gear like Onkyo still don’t get the prices, but are stellar performers. It’s just that they aren’t as iconic, so many collectors will pass them by.
Speakers are even more skewed, the best example I can cite is the JBL L100 Century / L100A. Very highly collectible, iconic, there’s nothing else like them out there in many people’s memories and they command high prices for a simple 3-way bookshelf speaker that was purposely voiced as a monitor, not flat, and just doesn’t compare to anything from a spec standpoint to speakers you can buy for 1/3 of the price. But, they are sought after for their classic looks and sound. They are art.
Do you prefer abstract art or still-life? Scenes with horses or portraits? Classical music or country? It’s all art, and nobody has a prescription from a Physician to buy a stereo system, so we’re all buying what we enjoy, and it’s all different. Nobody has to agree with my choice and I don’t want to convince you that I’m smarter, have better hearing, better taste, anything else. Nor does anyone else have to convince me, all I really want to hear is that you enjoy owning, looking at, listening to, posting about, working on, whatever it is about your system and equipment that makes you want to own it.
It’s a great subject to discuss, vintage is climbing in many markets, and falling in others. Pocket-watches for example have fallen in value, I happen to love American Brilliant Period Cut Glass, ... its value continues to slip as the people who remember it are no longer collecting. What will a Picasso be worth in 10 years? Certainly I can buy a new print that has more stable ink for less.
My audio is worth nothing to me, unless it’s turned on and playing music, that is its value regardless of its age.