it's a FWD car, that spoiler puts down force to the back at high speed which generates lift at the front in which case you loose traction. you need a front splitter to take full advantage of the spoiler.
i have 68k miles and 30 something on the gt3071r, still runs strong even after two fender benders in the rear bumper, everything looks right though. there is one little sound in the rear right door, like there is a rock there or something.