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

I cannot attest to vintage vs new but feel compelled to assure you there are SQ differences between DACs.  I believe most have/would agree. My limited experience is using a Bluesound Node2i with my Audio Research GSi75.  The comparison of analog out of the Node to optical out is beyond night and day. 

Any R2R Dacs will sound good.
I like the Holo Spring 
Wadia 64.4
Sonic Frontier SFD Mk3.
I haven’t heard Denafrips 
As far as inputs i prefer SPDIF and AES/BU
The only thing the new Dacs have are
I2S etc. which I don’t find musical.

My first DAC was a new PS Audio Ultra Link... that was followed by an Ultra Link II which was much better. From there I moved into one box with a high-end Marantz player ($3500) I didn’t care for and sold after about a year. I replaced it with a Sony XA 5400 ES, which was a Stereophile A+ component and extremely good on Redbook and SACD. I’m streaming now with a Cambridge CXN (V2) feeding a Benchmark DAC 3b. I listen to lots of internet radio at 256 and 320 kbps and then go to Tidal and listen to albums when I hear an artist I like. The Benchmark is also Stereophile A+ rated. As far as source material goes the Cambridge and Benchmark are significantly better than the Sony and both are A+ rated. The only thing I would add is that I spend lots of time on wire and if you haven’t spent time with different digital cables (and interconnects) you don’t really know what you system sounds like. I’m presently using the best of 9 digital cables tried so far and have #10 coming to try. Funny thing is #9 is very popular in Japan but not sold here, #10 is a 75 ohm digital cable also not available here

Where I think you will find significant differences are not necessarily confined to tonality, the differences are quite apparent in the sound-stage presentation. Width and depth of the stage ... the definition of performers outline and their location in the performance, not only side to side but front to back and their isolation from each other within the performance, as well as the layering of depth of stage. These are the areas I have noticed huge improvements in with one of today’s top DACs while still using the same amps, speakers and pre-amp as I did 25 years ago.

Does not age well.