there is plenty that can be gained with work to an s2000, the question is what is the purpose of the build. dropping the stock exhaust for a lighter single or titanium system not only frees up a few hp but also eliminates quite a bit of weight. a good intake and header along with some tuning to go with the exhaust will net you in the neighborhood of 20whp...you won't really need much beyond that. all the large companies produce suspension and chassis parts as well to stiffen up the handling. the aftermarket is large, just many people aren't aware of how big it really is.