Why? You want large metal beams running through your car when you're in an accident like that? Try wrapping a baseball bat with foam or rubber and have your friend hit you upside the head. Thats a rollcage in an accident.
Man this is an old thread, I had to go back and re-read what I said. Its getting to the point where you have to go to AZ or TX to have a Fox around here.
I think a cage would be "safe" if you wear a helmet... which you don't on the street. Maybe a 4pt wouldn't be that bad, only if you don't carry any rear passengers.