Stock Rules on Roll bars:
13.2.H. Roll bars and roll cages may be added (See Appendix C). It is strongly recommended that roll cages be constructed according to the GCR, though they must be bolted (not welded) into the automobile and be contained within the driver/passenger compartment. Roll bars may be welded in. A roll cage has more than four attachment points to the body or frame, or has bracing both fore and aft of the main hoop.
Appendix C (pg 217-219) includes a lot of basic roll bar guidelines but I think that this line is more about what you are asking about:
"The basic purpose of the roll bar is to protect the driver in case the vehicle rolls over. This purpose should not be forgotten."
a lot of the time for a Stock class car, the weight of a roll bar/roll cage is a greater deficet than any stiffness that might be gained (like Steve said)
I think you have hit upon a big thing that most new people don't understand. Asking questions is the best thing that you can do. And we will try to answer you questions, so keep them comming
