Doing the bushings to improve handling is a good start. There's some discussion around whether to use rubber or a polyurethane bushing of some sort. For a canyon carver, I use PST's polygraphite. It's a little harsher and a little sharper than rubber. I don't have the squeaking issue that some have reported with other brands.
If you're going to be doing some serious canyon carving, I recommend either a Panhard bar (aka track bar). The bar limits the lateral shift of the rear axle when the car is turning. Although new springs will help, under hard cornering, the axle tends to want to pull them over allowing the tire to contact the spring and/or the bodywork of the car.
I personally am not a fan of the Panhard bar because it limits suspension travel more when turning one way than the other. I recommend the Panhard bar over the Watt's link because the bar can be purchased off-the-shelf and is fairly easy to install.
