Kevin -
The definition of "suitable" is so varied... I no longer own the Mini thanks to some dumb bimbo in a 4Runner. So I am taking the X3 since that is all I own right now. As you may note from this forum, I have been running the X3 with BMW CCA Auto-x and doing fairly well (all things being equal).
While the X3 is not my absolute first choice for a track day it should be fine. The key is keeping the vehicle within its limits. Based on its performance auto-crossing I should not be holding people up too badly out there
Frankly, there is no good reason not to go. Visit your local rental agency and rent a miata or something for the week-end. Many places even rent BMW's (a friend of mine is planning to rent a 545i)!
This event is being run on big Willow. I have never driven that track so it should be exciting. While I am nervous as hell I think it will be great. Think of it this way... if I have an off-track excursion it will be no big deal for MY car
Anyhow it would be great to see you! Since it is an overnight bring the wife (I hear Lancaster is a great place for a honeymoon).