my car is similar, and it got worse with new tires (went from cheapo to good)
I'm running 16" GTA's with 245/50-16 on the front.
I went to the alignment shop with the results of my searching on here.
"Lots of caster, please." They had to send a kid out for more shims....
It seems with the extra caster, that the cross-caster (difference in caster from one side to the other) is making the car drift too much. I believe the cross caster is intended to make the car run straight on crowned roads. With lots of total caster, the cross caster works too well and the car never goes straight.
I want to get back into an alignment shop and play with reducing or eliminating the cross caster and play with toe settings. There should be a way to get the car to drive neutrally....
Some groove following is ok, but the current condition of the car is annoying....
Bob
(any alignment techs on here?)