There are still 70's bikes sitting in garages, waiting their turn in the next garage sale. Most of them bike boom garbage but always a diamond here and there.
Now if you really want to have bad dreams, think about buying vintage bikes thirty years from now. One steel frame on eBay, twenty aluminum ones and fifty carbon ones. And the steel one is a fixie conversion of a Bianchi Eros and it's got white Deep-V rims, pink chain, and NJS-certified cranks and stem.
I hope people keep wanting to buy those awful Stingrays; it'll mean fewer dollars chasing my favorite bikes. The people buying them have no intention of riding them, nor do their grandchildren so in a few more years I predict a beanie baby type drop in the Stingray market.
The rising population of the world means there will always be price pressure of some sort on all kinds of things, even Varsitys and Motobecane Gran Tour de Luxes.