Originally posted by Adam I don't think there will be a substantial increase. Demand may have some effect, but prices will be kept in check by the superior performance of modern lenses. As the D FA lineup matures, I'm sure there will be some bargains to be had, even among formerly expensive AF lenses.
I agree and would add that Pentaxians already knew what the good performing legacy lenses were, and this isn't changing with the coming of the K-1. The good glass on APS-C is still good glass of FF. It doesn't help that many of Pentax's legacy zooms are not great - modern zooms are worlds ahead of much of the film era, and if you compare the new DFA zooms to the high end FA zooms the difference is stark (who would pay near DFA 24-70 prices for a FA* 28-70, despite the FA* being premium glass of that era).
Primes are different, Pentax has long had a good lineup of excellent primes, but without a sudden influx of new users I suspect the prices already reflect the quality premium given the size of the market. And sadly for those garage sale resellers, the many 50mm f2 manual focus lenses are not sudden going to be worth $100 (sorry folks!).
There might be some movement with those lenses which didn't fill a niche on APS-C but do on FF (FA 20-35mm, I'm looking at you as the cheaper UWA option), but I'd expect them to be small movements that will level out before long anyway.