I agree with Chris on this one, bottoming out your springs isn't always a bad thing.
Some people bottom out there springs a couple times and then decide that it must mean that they need the next weight up and therefore buy new springs, when they bottom the next weight out they want the weight about that.
Its finding the balance between the effort you have to put into bottoming them out as well as the fact that your bottoming out.
I've been on raptors for nearly a year now and have been able to bottom them out for nearly a year now aswell, but i've only just decided to get stronger springs because I loved the fact that i could put soooo little effort into my jumps and a get an easy couple of foot air.
With the T-rex's i'm going to upgrade to, yes i can get higher on them but i have to put a lot more effort into bocking which will probably mean in the long run i will get tired much quicker.
Thats my 2 cents, for what its worth