Rogue,
Although swapping out a set of coils for air springs will considerably help the ride quality and handling, it will not make it a road racer. You must also upgrade shocks, sway bars, control arms, tires, etc. to really make a car corner well. And like Tony said, make sure you use a 4 way valve. On an extremely heavy car like yours using a 2 way system will allow
tons of body roll. Literally.... tons!
We are hosting Auto Cross's at many of the GoodGuys events next year. Stop by and we'll give you a ride. I heard that we have scheduled a Steet Challenge Auto Cross for the Costa Mesa, GG show in March. So all of you West Coast guys will get your shot!