I expect great new releases will continue to erode prices on older, less desirable pins.
Isn't it more likely that Stern will be able to continue to sell great new pins at the current price?
If those new pins end up taking up space in collectors basements, and those collectors are forced to sell some of the existing pins, then the older titles will be in greater supply, and will then command less money.
Those newer Sterns that were recently unboxed will still be worth most of what a buyer paid for them.

I think the supply and demand will be title by title, not "the hobby as a whole".