[ray]

The reason people are going to larger rear bars is to effectively stiffen the rear of the car, reducing rear grip, and thus reducing understeer. To increase the size of the front would negate this affect, as the front would now be as stiff relative to the rear as it was when stock. If anything you'd go to a smaller front bar, to produce more grip in the front and reduce understeer. The only problem with this route is body roll would increase, necessitating stiffer springs to control body motion.