Are "vintage" DAC's worthwhile, or is this a tech that does not age well

@miglos,
1 High quality good sounding vintage DACs can hold their own against many of the current generation DACs. A lot of the very good older DACs were well engineered and have very good power suppliers and analogue output stages. What they'll often  lack is modern connectivity and flexibility.  If your main listening is Redbook/16/44 you can obtain excellent sound quality. 

2 I can appreciate differences in DACs as easily as I can with different cartridges or other audio components. I reject the "all DACs pretty much sound the same" not by a long shot.
Charles 

@charles1dad +1.

My current DAC and the one in my friend’s system (Michael Spallone, who modifies the Synergistic Research MPCs here and the other site), both have NOS DACs with older chips and we’re thrilled.
Michael’s system is the most three dimensional and holographic system I’ve ever heard with unbelievable depth.
Oh, and he doesn’t even have a standalone DAC, he has a CD player.

You did not say how much you were planning to spend. I would not invest in a old dac though 
but a nice R2R dac like a Holo springs May dac,
Denafrips R2R dacs ,even black ice  audio burr brown tube dac ,Topping 9
many options depending on budget to spend ,many prices and different flavors depending on your audio systems sonic signature.

I have found that at least on the few dacs that I have tried that you can put a very good modern USB to SPDIF converter in front of it and get excellent up to date USB performance.  Also,  I purchased a SMSL M500 Dac and was pleasantly surprised at its performance.  It definitely out performs the other in expensive DACs that I've had in my system. and believe me, I wasn't delusional.  The differences were very audible.  I have now owned 11 different inexpensive DACs,  many were similar, but some varied wildly.  

I am listening to a Dac built in 1995 and it sounds sublime. There's a lot more to Dacs than the latest digital technology.