Rear Torsion along with the sway's will do you some good. About as good as you can get without rollbars. There's also some sort of frame stiffener (sub-frame brace(?) I think its called that) that is applied dead center somewhere along the path of the exhaust. Not sure if it's worth it. Get some strut bars, maybe? If you don't use your trunk much, it'd look cool in back as well. Definitely would help out with the car's 60/40 feel.
Not linked as to purchase, just to educate/give ideas of different ways of stiffening ride for kinda cheap. There's plenty of spots to brace the car more as it is shown, but not all of them are worth spending the time on. Our platform already has decent rigidity.