I have lowering springs, sway bars, strut braces, lower stress bars, flame stickers, muffler bearings, CAI, re-flash, TurboTorque, Tornado (just kidding on this one) and a whole bunch of other stuff and in hindsight the only thing I think made a HUGE difference was the
TBD (LSD) and some Hoosiers. In my opinion you should consider this the first major upgrade before coilovers or GT3 lower control arms, or anything else. I believe that the primary reason the S2000 has been so competitive over the years is because it has the LSD to help it around tight corners at lower speeds.