I like that idea ... I'll feel more comfortable sanding a $0.10 screw than drilling out 10 holes on a $70 chassis. I do think that some of my screws have the thicker than usual head.
Even with a brand new belt, with the front diff on the center setting, I can push the belt down a good centimeter easily, probably more (not at home now to do the measurements). I think belts can be run a lot looser than people often think and I'm probably dealing with chassis tweak more than the belt issue. It's just that my old belt (which admittedly had been in there a while) was pretty beat up, but it could have stretched too.