Old SS amps

They are excellent to use as a trade-in. If a classic, sometimes you can get back nearly as much as you paid for it. I had a Pass X350 which I got all but $500 back after nearly 20  years. What a great investment. 

I got a significant trade-in for my Threshold s/500 as well. 

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!!

Those who don the rubber gloves and wellies and are with the adeptness to build Valve Amp's in the Modern Day, will get quite excited if Iron is found from the 1930's.

Shoe Box Size Tranx''s from the 30's, working with modern Components and Valves from the 40's, is today being realized and I meet the odd individual keeping the Art and Themselves Alive.

A Friend during their earliest interest in Audio, had acquired enough Quad II Amp's to fill a few shelves in their Mancave, they refurbished these and made monies to Upgrade when making new Purchases, some would say the Quad II is all one needs. Not bad for a 1950's design. With Horn Speakers they did quite a nice job.

Another Friend is using Sansui AU 111 with a complete overhaul of Parts as their main Amp's, these 1960's Amps are adorned with Valves from the same era and are driving Stacked ESL 57's, there is a substantial amount to like with the EAR Acute as a Source, also adorned with 1960's Valves.    

 My Own Valve Power Amp's that are in regular use, are a design completed in the 90's and built during the late 90's / early 00's.

Today I am able to listen to quite a few Valve Amp's designed / Built in the 90's era and am always thoroughly impressed. One Owner bought into a design for very very fair monies, with a Mirror Chrome Casing and Interstage Tranx's incorporated as part of the design. This has been compared to currently available of the Shelf Modern Design Valve Amp's used in the same system and has shown itself to be a Kick Ass Amp'. The owner of this Amp' does not need to Spend an extra £6K - £10K to get something quite similar.

Another Friend specialises in Overhauling SS Japanese Amp's from the 70's to the 90's. Amp's overhauled are used in certain Systems where other supporting devices are approx' £30ish K in Value. I am associated with a few of the owners of these Overhauled Amp's, and know the Owners are not in any frame of mind to change, they proudly wear their Amp's used on their Sleeve. I am very very Familiar with a Overhauled SS Sansui Amp' from this era, there is nothing to suggest it has shortcomings that are discernible. I recently added one to a Shortlist to be used as a Amp' in the SS System to be produced for my Wife, for her to enjoy her Vinyl Collection