You know, car analogies abound in audio, and I'll resist making another one (say, comparing performance of a Subaru STi to a very expensive high performance luxury sports car and asking the rhetorical question why would anyone want to pay 10X or more for the almost the same acceleration, etc.).
But, this raises a slightly different issue to me, analogous to cars: that is, few of the 'flavor of the month' products have lasting value and are actually worth more after 5 years. I guess you could say, in things audio, that the 'technology' keeps improving, so that there is little value in older gear, but it is an interesting question to me, and not really what Taters asked.
Sure, Marantz 7 preamps, the various amps and the 10b fetch more money today than what they retailed for 50 years ago. Perhaps there are a few others, old Quads aren't expensive to buy restored but they are still a multiple of what they cost new, and that's probably true for most antiquarian equipment, e.g. old WE stuff, Klangsfilm, etc.
But, are there pieces made in the last 10 or 20 years that fit into that category? A couple of John Curl's early phono stages?
Not suggesting that high end doesn't have long term value, but it did get me to thinking....