I'm still very much a newbie myself prettymuch, but a few things I can suggest straight off the bat that I've learnt from my Evader BX.
First.. get rid of those stock rear tires.. they're WAY too hard for most tracks. Get a set of proline 2.2 holeshot M2 or M3's and you'll find it'll help a lot.
Second.. switch all your plugs over to deans plugs - if you haven't already.
Thirdly.. make sure your buggy's suspension is set up right. Ideally you should have it rest so that the struts and turnbuckles are horizontal after giving it a downward push and letting it spring back.
Fourth.. get that battery back a bit - it'll help stabilise your buggy a bit over jumps and in turns. I pulled the foam out, chopped a bit off the end and made it inline with the back of the ESC.
I've also changed over my motor to a Monster Stock Pro - which means I can compete at the local track in the stock class. I've also since picked up some 30wt Shock Oil and found this works well.
There's a few evader websites out there you can check out -
Racer9 has some good tips on his, http://www.geocities.com/jep_rc/home.html
Jep-RC has some nice strong replacement bits for the evader BX on his.
Mis-behavin also has some useful tips under General Info.
The evader is a cool little buggy. It's fun to drive and does pretty well for itself I reckon.
I've just ordered the rear sway bar kit and carbide thrust/diff balls for mine, along with a few other bits and pieces and will see how they go. Also just bought myself a nice new radio (JR XS-3) but haven't given it a full workout on the track yet.