For me the question becomes what do I intend to
do with the bike?
if I want it for private collection, never to be ridden
I'd leave it alone. This is especially true of something with
historical significance, say Fausto's Bianchi.
If I were going to show it, send it off to restorer
(Brian Baylis, Jim Bell) to be made new again (they can
replicate decals etc.).
If I were going to ride it, I'd clean it up a bit but leave
it in somewhat original condition.
If I had the desire to repaint, put on current drivetrain
(ergo, sti, whatever), I'd sell it to someone who would
appreciate it for what it is.

Marty