Just my opinion, but I think there is no doubt vintage bikes are going the way of the model train. Sure, you'll have onesies and twosies of younger folks who get into it, but their numbers will be significantly less than current enthusiasts (or, at the peak, the number of enthusiasts of the mid/late double aughts).
A perfect analogy.
There are some high-end collectible Lionel trains from the 1950s that still command high value, based predominately on condition. But I am able to buy less-perfect pieces today for prices that would have been unheard of 30 years ago. The guys who had massive collections of trains are dying off, flooding the market, Kids today generally couldn't care less about model trains. So...a boon for me, but not so much for the guys who planned on lavish retirement living by cashing in on their "investment."