Old Amp vs. New Amp

Just to make sure, you are talking about amps specifically and not receivers, right?  I only ask because I see this become a misunderstanding too often!

That said, it all depends on what 90's models you are eyeing, the 90's had big changes as some manufacturers started production in China.  Generally speaking though, a good quality amplifier from the 90's could be a viable option today.  Just remember, an amp that has 20 years under its belt could develop issues.

Okay, I have no direct experience with those brands you mentioned, but since they are top line brands, I think you'd be pretty safe with them.  My own experience with Nad is with the 326 and C356BEE.  The 356 is better at higher volumes, but when I compared it with a Parasound A21/P7 combo, the Parasounds kept their composure when the Nad was reaching its limits, and were only slightly better at lower volumes. This has made me curious about the Nad C375BEE.

Anyway, these brands are always suggesting that they've improved and have something better, but I agree that it's probably more marketing than anything else.  I am a believer in good cables, however!

I should probably qualify my cable comments.  Personally I'd never spend $1000 for a cable.  I currently have 2 pairs of IC's that cost about $300 for both.  My Wireworld speaker cables cost about the same.  These both brought improved sonics for me and I'm happy there.  

As far as amps go, I'd concur that you could get more value in a used one while not losing out on sound quality.  Amps are a mature technology and as long as you get a well built one, I'd suggest you'd be fine.  

The Parasound gear I have has a slightly warm sound, with the top end probably rolled off a little, and I suspect the P5 might have the same characteristics.  I've read that the Nad's sound is similar, so when amp shopping, you may want to avoid amps with a warm sound, and go for neutral or forward sounding instead.  Unless of course you prefer a warmer sound.