Most of those mods are there to make the car more predicable and consistent. Those are magic words in racing. The best handling mod you can do is get good tires that can grip. You can drop 2 seconds on an autox course with tires alone.
I disagree - the best handling mod you can do is the driver mod. Second place is get good tires, and everything else is way behind from there.
Also, remember that the stock Kumho's were stated to be good for 0.80g on the skidpad by Car & Driver, while the optional, same size Michelin PSS's tested at 0.90g. A tenth of a g in lateral acceleration is an epic difference. PSS's or similar (or R-comps) should be on every real enthusiast's short list of stuff to buy. Restated, if you think you're a serious enthusiast and you have stock Kumho's, or any other economy or all weather tire, then you're not a serious enthusiast, and all the money you've spent on coilovers and other stuff is wasted because your tires won't let you make any real grip. 0.80g is the lateral acceleration of a pickup truck.
Also, when I get this yahoo out on the open track later this year, I will be bringing my GTech RR to do some logging of lateral acceleration, just for giggles. Plus, it will help give me some concrete numbers, turn by turn, which I could compare in the future should I decide to make this car the dual purpose machine and get some track wheels and tires. I just might need to make a custom mount to the passenger seat rail or something, but I really want to bring it. I also want to log the OBD2 port with my logger, but that's probably going to be a little more difficult to get past tech.