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

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.

The job of a DAC is convert the digital signal to an analog signal without loss of information and adding audible distortion and noise. There are DACs from fairly inexpensive to outrageously expensive that can accomplish this and have been able to for quite a while now. It is possible to hear differences in DACs but it isn't easy unless the DAC has been purposely built to distort the signal or the DAC is simply junk. The reason it isn't easy to tell DACs apart is they generally measure better than your other components. Amplifiers, pre amplifiers almost always will have more distortion than a DAC, even ones that measure well. Speakers are the weakest link they swamp everything else. Add your room acoustics to the speakers and it's very unlikely anyone hears differences in competently engineered DACs. If they tell you they can ask if they listened with their ears only or their eyes and ears in other words did they pick a DAC better than chance without knowing which one they were listening to. 

If you can't distinguish the sound between a $100 dac and a $1,000 dac you better get your ears checked and get the wax taken out, and you're an idiot for saying that, obviously your system isn't good enough to be able to hear the difference. LOL

Heavily modified MSB Link DAC and outboard power supply here. Very, very nice sound. Picked it up for a song. Only downsides are 2 inputs and missing input switching via a switch or button. Sound quality wise, it is unbelievable.