I figure if the paint and vast majority of parts are original, leave it be. I have a 67 Rams Horn 5 sp fastback. It's original (repop chainguard) and shows scratches, surface rust, ripped seat, that kind of stuff. All I've done is got new fastback-correct Schwinn repop tires on, and kept the shifter/derailer and brakes working. Obviously keeping it clean and polished up is very good. I see no point in restoring this one, its just barely too nice IMHO.
now my 68 StingRay is custom, but I started with an almost bare frame still sporting much of its original coppertone paint, and collected parts from other basketcases to make it what it is. The repop non-original Schwinn stuff is the springer setup, rear slik, pedals, headbadge, and seat. Everything else is rechromed/rebuilt original parts. I think of it as a kind of "what-if" specialty bike that Schwinn could have made with off the shelf parts in 68.
Regarding the 67 Schwinn StingRay Lil Tiger, I am customizing it to match the 68 color-wise. This bike was complete minus sissy bar, but all original; the original coppertone paint very scratched up and the whole bike had droplets of white housepaint on it here and there. The tires and seat are really nasty, the chrome is shot, fenders bent...
Despite what i doing to the Lil Tiger, nothing I will do to it is irreversible; one can easily paint over copper plating.
So thats my take on it anyways.