On the caster block issue, I don't know what to say. The only other thing I can think of is that the king pin screws are not going in straight enough and causing problems. I've only broke a couple blocks in 2 years and had some very heavy hits. Most of the time if I've broke a block, I've killed an arm and maybe more. Do you have a P-dub front bumper. If not, that may help. They take a lot more impact than the stock bumper.
As for bodies, like heavy said, the better you get at driving, the longer your bodies will last. I usually go through bodies in 3-4 months. But I stop running them long before they're completely done. (although I killed a brand new Stratus 3.0 that Lynn had just painted a couple of months ago.
) Small cracks and scratches are no big deal. I like the Mazda a lot right now. It seems to flow through the corners the best and seems balanced better than anything else. Most of the other bodies either have tons of steering, or not enough.