Some of us are content to leave well enough alone, some of us never can. I really enjoy people who hot rod small engines. I grew up with air cooled VWs. The late model 1600cc dual port engine was fabulous, ran all day long at full throttle if you wanted. Every piece of the engine and drive train were balanced to all the others. Yet some people just need to tinker and port, polish, bore, stroke, turbo, etc. Sure, you could just get a bigger engine and bolt it up but where's the fun in that?
Me? I usually work on suspension first. It seems to be the weak link in every new bike and straight line speed was never my bag.
Scott