Old SS amps

So at 20 years there was still a market for it so that people were not reluctant to purchase it?

20 years is not old for high-end quality amp and replacing the capacitators is not a big deal. You can have it done at a reasonable cost, many times locally. Over the years, I have had at least a dozen amps recapped. 

I bought an Acoustic Research Amp new in 1969.  I recently gave it to one of my sons and it is working OK, though probably out of spec given the age of the electronics.

I have an ADCOM GFA1 I bought new in the late 1970s in storage I use for backup when needed. 

I have two Carver M 500t amps circa early 1980s currently in service in an office system and in an AV system for surrounds.  Both were bought used.

Not to mention more recent buys.

Vintage? Dude, vintage is 1960s tube amps.

This answer depends on the brand and the level of support.  I'd pick up the phone and talk to the company what you are thinking of buying to make sure they will still work on them. 

Pass labs, Parasound, McCormack and others I would not hesitate at all to buy an older unit since I know I can get service (caps replaced) if needed.  

Mark Levinson, Krell, Classe no way, at least not now.   I've been down that path and service is just too much of a crap shoot.

Good luck!!