There is no doubt that chassis braces alter the "feel" of the car, but there is a lot of debate as to whether that alteration in "feel" equates to faster lap times.
My opinion on the subject is that if you are looking for those last few tenths of a second in a turn, bracing the chassis may give that to you. but if you are just starting to set the car up, there are a lot of other things that need to be looked at 1st.
But then tuning for the street typically is more about tuning how the car "feels" then how the car actually handles.
it would be a hell of lot cheaper just to run a 1/4 tank of gas and take out the spare tire and jack and the track and i am not being a smart ass when i say that. putting on a 22mm rear sway bar will yeild you better results at that to.