Great thread Jim!
Some eloquent responses here to a complicated question. I think we are learning in this thread that there are different reasons for different people to be drawn to older bikes. So some folks love Schwinn Varsities and some think they are low-technology boat anchors. Some appreciate brifters and put them on bikes that originally had friction shifters: Others scoff at such hybridization.

For myself it is a complicated mix. Part of it is that I understand the technology and can repair it. Another part is the aesthetic appreciation of certain components and frames. Part is the familiarity and continuity from my 20-year-old self, riding on those older components to my current 60-year-old self riding the same components. For me certainly the "auratic" nature, described by DIMcyclist, of a hand-made frame, whether it is old or new is huge - the appreciation of something that was made by human hands: If the owner of those hands has a similar aesthetic sense to myself then that frame calls to me all the more powerfully. If I know the owner of those hands personally the call is pretty much irresistable.

Another important factor is that this shared passion allows me to be a member of a diverse community like this forum and share the experience with others.

I also own and love modern bikes, but for a somewhat different mix of reasons.
Brent