Valentino,
A poorly maintained instrument that's 30+ years old will sound totally different from a new instrument, too. But this would probably not be characterized as in a good way.
Wasn't there a super-secret mil-spec IC that went in to the early models (used until the supply ran out, since the manufacturer stopped making them)? This was, from what I've heard, at least part of the magical sound of the 70's era instruments.
With regards to apples and watermelons: for any two items, there is a comparison that can be made that is simple, objective, and incorrect.
Brad