When you hit 99 gold bricks, you think you'd get an amazing new world to explore! No such luck. What you get is an infinite coin tower, which eternally pours out piles of studs. You just stand beneath it, walk away (you the human, not the little lego character) and when you get back from lunch you have 4 *billion* studs in your inventory. That's the max that you can get. Of course, since there's nothing left to play, and really probably not much left to buy, I'm not quite sure what the point is :)

Lego Star Wars 2 Walkthrough