You should come autocrossing with us, its pretty fun.
As for advice, there is always swapping the motor. About damn near everything has been swapped into the RX-7. Grand National V6 turbos, LS1's, Ford 5.0's and 2.3 turbos, another rotary...your options are pretty much endless in that regard.
If you want to make it handle better, Racing Beat sells a reasonably priced suspension kit.