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

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.

FWIW I tried a few of the top DACs recommended by Audio Science Review from Topping and others.  Thought they were clean and measured well, to my ears, they were completely uninteresting and added nothing. To many that’s exactly what they want and I can’t fault that. However, I ended up with a MHDT Orchid using a “vintage” NOS DAC chip. It captured more of the “analog” and “vinyl-like” smoothness and life that vinyl has and added something to the music which I enjoy and which the Topping DACs did not possess. An engineer or a measurements fanatic might cry heresy but hey, it’s all about what sounds good to you. 

Agreeing with above. There’s only so much you can do with A/D conversion of 0’s and 1’s, as proven from being in studio sessions hands-on. 

Different DAC chips and different implementations leads to different sounding DAC, sometimes it's subtle, sometimes not. I experienced enough that I cannot take seriously anyone claiming the opposite. For example the W4S DAC-2 and ifi Pro iDSD sound very different, and the difference is easy to notice within seconds. One is neutral-cold while the other leans more on the warm side.
Perhaps some people start to have enough of cold and analytical modern DAC and think that vintage is the only way to go. But some modern DAC do sound musical and engaging and are not that expensive.