After racing a bit I can tell you that a proper shock can make all the difference. There was a VW that could fly off the jumps, and it was all shocks. You can go with either an additional lift spring or a stiffer shock, depending on what you are trying to accomplish.
Does it only bottom out on sharp bumps, but ride smooth the rest of the time? How does it sit on the springs when at a stop, is there a slight positive arch to the springs, are they flat, or is it a neutral arch?