You can take any kit and make it do the job you need. It's all in the tuning and head selection as well as how you treat the track. Rock tends to use less muffling (see that dead horse over there, let's beat him again!), lower tuning and more ambience or effects. You need to experiment a little before shelling out dough for a new kit. (Unless you just really want one, which for me is as good a reason as any.) If you get a new kit and tune it the same way your old one is tuned, it'll sound about the same. To a mic, a drum is a drum is a drum pretty much.
Different shell materials, how bearing edges are cut etc. also have an effect on the sound. There's plenty of info if you do a search here.
