This subject does come up every couple months, and the general consensus always seems to be the time will come when no one interested in cars is still alive and a hemi cuda convertible will be lucky to sell for 10 grand.
I don’t have a crystal ball, but I do know that for any given hobby there are a lot more people not interested in it than are, so are no kids today not interested in cars, or are most not interested? If none are, the hobby is doomed, if some are, the car hobby survives. I remember in the 80s several instances with people and my T/A, where friends said something to the effect of why would you want that? To hear everyone here talk now, every red blooded guy in the 70s and 80s was into cars. I was, I had friends who were, but I also knew far more people who couldn’t understand why anyone would want anything beyond a good point A to point B ride, or else something new and expensive that might attract girls.
I can’t imagine there are too many people around who are gung ho about Duesenbergs, and few alive who were around when they were new or late model, yet they are still worth a fortune. Other cars like Model Ts seem stagnant or down in price. Lots were built and they are quirky to drive in traffic. At least muscle cars don’t have trouble doing the speed limit! And many muscle cars were low volume and survival, which means even if 99.9% of the population has no interest in them, the .1% that are might be enough demand vs supply to keep values from dropping.
I’d be mostly concerned about drivability issues affecting interest, but the popularity of EFI and disc brake conversions for older cars, along with adding AC, suggests to me that many enthusiasts are adapting to keep their cars comfortable to drive rather than losing interest in old cars.