I was looking at getting this kit too. They say it was developed for the added weight of the Roushcharger and Roush wheels. While I don't see the Roushcharger in my future at this time, I do like the TrakPak wheel (Wheel + Tire +TMPS = $1K/corner!!).
I wonder how the car would behave if you don't have their wheels or blower...
Is the Stage 2 that much different from the Stage 3?