problems with suspension/tires

[Miataracer]

hey guys, when i was looking my car over the other day i noticed something interesting. it seems i am wearing off the inside edges of my rear tires. now I am well aware that this is a common problem with lowered cars that have not corrected the camber, but the weird thing is my car is at stock ride height. i am not really sure why i would have so much negative camber at stock ride height that the inside of my tires are wearing off. also, they are both wearing in the same way, so its not like only one tire is wearing out and not the other. my car has over 180,000 miles on it now, is it possible the bushings are so worn out that it just cant hold proper allignment/camber specs anymore? i want to get this handled so i don't wear out any more tires!