I put in a front strut tower brace from TANABE, I think it was around $120. It helps under hard cornering, but it makes a very minimal difference for around town driving. I have considered the rear brace, but don't want to be limited in what I can carry in the back....I have heard that those things are expensive...especially if you go with the one from Subaru. Aftermarket would be the way to on this one.
Honestly, aside from the 19mm RSB, the biggest improvement I have done is increasing the tire pressure to 36 front/34 rear. It really tightened up the "turn-in" lean that really annoyed me on the OB. It also made the car run more true/straight at highway speeds (ie: less squirrely). This is with the stock Contis, so since the OP has already changed out his tires, not sure if this will help.