I don't know much about spreading the rear as I have no need. Barring any limitations, if one is willing to add a new group to an old bike wouldn't they also have minimal concern with cold setting?
Also, it does appears 80s-90s are more sought after by younger since they appear more modern in ways and have more options for gearing and styles. I prefer a good amount of the 80s myself. But collectors of multiple bikes that are not just wanting to ride an old bike will still be out there.