All sorted now. I will give some more detail in case anyone runs into a similar problem.
GPU settings may have been the problem after all. I always keep my drivers up to date, in fact I'm slightly obsessive about such things. :-) Turns out that may have been my downfall. Out of desperation, I made some changes to my Catalyst profile settings and presets. I created an application profile specifically for PCS, and made all settings application-driven instead of being forced. Somewhere along the line, one of the changes worked, and all models now display normally again.
My guess is that PCS didn't like the forced value of one of my profile settings, but whether it was AA, AF, texture quality, v-sync, buffering, or something else, I cannot tell. Hopefully this knowledge will prove useful to someone in future.
Thanks to everyone for the replies!