In the 1970s, nobody I knew had much respect for Fender's offerings. Pre-CBS was in demand then, just as it is now, but for a different reason. Then, pre-CBS was higher quality and would get played, not collected. If you had a 1966, it was just a bass, since it wasn't pre-CBS, and chances are you flogged it unmercifully. Which is what should happen. Now, all those crappy 1970s Fenders are expensive and vintage. What happened? People forgot that they couldn't stand them at the time. The sloppy neck pockets didn't shrink and start to fit. Sure, they play well if you set them up right, but they are just old now. A current MIM is probably far better made than a 1970s Fender. Go look at both up close.
The wires shouldn't change. If they do, you are screwed. The magnets get weaker, so the sound changes because of that. Wood continues to crystallize, but I wouldn't expect that to make much difference in a sold body instrument, whether it's a Fender or Gibson or something else. A hollow acoustic instrument may sound different, but I doubt it's all that significant with those, either.
I can't cite it, and I'm too lazy to fire up Google, but there was a blind test using Stradivarius violins and newer ones. They were given to virtuoso violinists to play and rate. The Strads didn't do too well in that test, since nobody could hear with eyes or pedigree. I have a couple older instruments, and I like them very much, but there's no reason to believe their age makes them any better or worse than anything else. Build quality is build quality, and some times, "they don't build 'em like they used to" should be followed by, "thank goodness they don't."