Once you max out the bolt-ons, you need to dump weight all over the car to pick up more effective power (and better handling): the obvious priority targets are tire/wheel weights, battery relocation/downsize, and gutting all the audio gear from the car and all the junk in the trunk area in general. If you want to keep all of that stock and you don't think the full bolt-on arrangement will make enough power to keep you happy, you might want to look at a low-end SC kit (by low-end I mean conservative pulley and tune, not cheap knock-off brands
). Better to go that route right off the bat if you're ever going to, since many of the best bolt-on NA stuff isn't really SC-compatible (e.g. big headers and long-tube intakes).