It's very hard to judge Imo, the comparison with old cars is the closest we've got to compare with in cultural and time scale, the same thing was said thirty years ago about really old stuff 'veteran' as it's now called, people thought once no one had living memory of those cars the value would drop quickly over a ten to twenty year period, who thought the guy with the Sierra with a body kit and massive turbo during the 90s would be into cars from the Edwardian period within a couple of decades? But it happened, prices have gone mental.
Look at antiques that don't do anything useful like paintings or items rarely used like ink Wells and hat pins, plenty of people still collect them just to have on show, which for many 70's Fenders is about all they are good for anyway, lol.