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

Does not age well.

I have a Kora Hermes II (tube DAC) that is very analog sounding. It’s gotta be at least 20 years old?  I put a couple of 1963 Bugle Boys in it and love the sound. Some May wince when I say it sounds very analog, but its smooth as silk and clear as mountain spring water. I know-weird analogy?

My dac progression went from Audio Alchemy to Theta Pro Basic to Audio Aero Capitole 24/192 to Antelope Zodiac Gold +Voltikus to Zodiac Platinum + Audiophile Clock. They all were converting bits but they don‘t sound the same.

Here's the right answer:
DAC's before 2010 were almost universally worse sounding with Redbook than with high resolution files. 

At a certain cut-off DAC's at all price ranges got universally better.  Performance with CD quality jumped up and digital glare and other issues vanished. I suspect this has to do with much more accurate clocks and anti-jitter technology in the underlying silicon. 
So for DAC's, not streamers, there's a real difference around this time frame.

The other part of this, music services. are more prone to changing.  If you can get a streamer that is separate from the DAC, and your DAC is at least post 2010 you can get state of the art for cheap.

Best,
Erik