I read about this quite a bit so I wanted to chime in. My stock car has 30K miles and the rear would always squat and wiggle at WOT even on the highway. It felt very unsafe. I guess I attributed it to wheel spin due to 640hp going thru only two wheels. I mitigated it by rolling into the throttle, as I would at lower speeds when wheel spin would really the a problem.
In any case the steering wheel was a hair off center and the car has brand new tires, so I figured I'd get an alignment to make sure I get the best life out of them. These tires aren't cheap! Well the toe was out on all four corners. Now the car feels 99 percent more confident when I go WOT from highway speeds. Very little squat (to be expected) and zero wiggle in the rear. Make sure you have them give you the before/after printout so you know they didnt half ass it. Of course my local shop charged a "V tax" for my alignment.