Lifespan of amps and preamps?

Regarding the question of maintenance on your NAD and Adcom both are due for a recapping. A general rule of thumb is that capacitors have a life of between 20 an 30 years, regardless of how often the components were powered up. These parts have a significant effect on the sound quality and the sound of older gear declines gradually.

I just recapped my 24 year old Krell preamp and even though it was working fine and sounded good, the new capacitors make a noticeable improvement in the sound.

The B&W's are a little different story. They should probably be recapped too but for some reason capacitors seem to last longer in speakers. If you can pull out and disconnect the crossovers the cost to put in new caps may be pretty reasonable.

The big question is if you have an attachment to this gear and want to keep it. It will cost at least a couple hundred bucks to recap each piece of electronics and if you're ready to move on you could take that money and put it toward newer gear. If you still like this preamp and amp (they are both great sounding classic pieces) then the cheapest strategy would be to get the maintenance done and hang on to them. But from a purely financial perspective it will cost more to refurbish them than they are worth. The third strategy is to just keep running them until they fail which could take years.

It's been my experience that you could spend a lot of money and get just a marginal improvement in sound compared to a recapped NAD and Adcom. I moved from an Adcom GFA 555 to a Krell KSA 300S the the level of sonic difference was disturbingly low compared to the difference in cost.

Most good equipment is rebuildable.  New Adcom equipment is cost effective.  

Iv'e got a pair of Pass Aleph 2's that I bought back in the early 90's and have uses on and off since. I just emailed Nelson to see about getting them tuned up and he asked me what problems I was having, I told him none, I was just concerned about the age of the amps and he told me that unless I was getting excessive noise as in hum thru the speakers to just enjoy them. So that's what I'm doin.. :)

They are like the pyramids ancient history its time to move on.

I've seen a 'new in box' Marantz 8B for sale recently. But I think having some history/experience with a particular model/brand really helps take the mystery/risk away from buying older amps.

In 2009, I bought a Carver TFM-35 that was still sealed in the box.  The only picture the seller posted was the box exterior. At the time good used versions of the amp were going for about $450.  Since I had owned the TFM-15 new back in 1994, I thought what the heck and just bought it for the 'buy it now price' of $575.  

Well, the sound of that amp really was great! The only thing it lacked was some bottom end.  But it sounded so effortless and detailed...especially in the high end. All those years in the box didn't hurt it at all.  The caps were shiny and new with no sign of expansion. I actually wondered if the aging helped it.  

When I took deliver of my Don Sachs Kootenay, I compared them side to side.  And while the Kootenay was the better amp...it was not so much in the high end...the Carver was pulling in a tad more detail there. Let's just say the Carver wasn't at all embarrassed by comparison. And with certain types of music, they sounded almost identical...very weird.

There are also services that will update and bring this gear up to current standards.  Sometimes it's just nice to see old gear working so well in modern times.