Trends in value of vintage / used audio equipment?

The problem with many sellers of high-end audio is that they don't actually have to sell. They can afford to keep ridiculously overpriced gear ads up for months on end, polluting resale sites for other users. 

This contributes to a paradoxical market where dealers are often more reasonable and accommodating than private sellers.

As for McIntosh, it's the rare high-end brand that neither blows smoke up their customers' butts nor assume they are absolute cretins. For that at least, they deserve respect. Plus, their amps are pretty darn good.

VU meters are useful, too, all the more so on amps with dodgy power claims (not the case with McIntosh, obviously).

Meters warn you the amp is getting kneecapped before it actually happens. Bob Carver always had the good sense to put meters on his amplifiers.

Packing and shipping 500 or 700 lbs worth of speakers is expensive and not for everyone. Relying on the local market is usually an exercise in futility, unless your speakers are much sought after, or extremely competitively priced, or you live in a major metro area, or preferably all of the above. 

Maybe that's one reason the trend is drifting away from floorstanders and towards subwoofer-augmented bookshelves and monitors.