First off, the original poster said that he was looking for feedback from guys who track their Vs. By that, I shouldn't be talking, as I just got my V and have yet to track it. I'm working on the same mod setup myself. However, I have tracked A LOT (as in, probably over 300 track days) and I'm a test driver and writer for Excellence : The Magazine About Porsche.
I just wanted to chime in on my own generic track day mods/spends. This has been true with anything I've ever driven, including in tests for the magazine. I hope they help. (By the way, this is the best thread that I've seen on this forum so far.)
1 - I know it's annoying, but spend money on instruction before anything else. All you're going to do by waiting is form bad habits. Don't do it. Track Days 1-4 should be with an instructor. Then, start spending money on the car other than some core things, such as -
2 - Best bang for the buck that I ever use is Motul 600 Dot 4 brake fluid. It sucks to come in early because your brake fluid is boiling. This happens more often than the pads burning up, but that might not be the same with a 4,000lb car.
3 - Hawk makes awesome pads. It looks like these cars have great brake venting too. Again, brake fade sucks. It ends your sessions early. It's dangerous.
4 - These cars get hot. Take off that huge quilt of an engine cover and put on some Z06 fuel rail covers. Put a 160 degree thermostat in. This will require a tune, but guys like Frost will do them for $150. There are other things to deal with the heat too. Plus, the tune (for $150) will give you some HP and take out the stupid CAGS (thing that keeps you from shifting into 2nd sometimes).
Guys, the car handles well. Sure, coilovers are great and will be a benefit. But the car handles. I don't get why it's at the top of the list, given his question. Just my opinion. I mean, it ran an 8:22 on the N-Ring.
I also want to say that I've done some tire testing, and the best two things I've driven for street/track are the Toyo R888s mentioned above and the new Bridgestone RE-11s. Both are incredible, and far better at talking to you than the Michelin Cups. Most of the things that I mentioned (other than instruction) are not actually performance enhancers but performance prolongers (making up words is cool). But once you get that done, NOTHING will effect your lap times and fun like tires. Someone said the opposite earlier and I can't disagree more.
Paying attention to this and that, springs and bushings... it's all good. But before a real set of lightweight wheels and tires? No way. For example - I had stock 19s on my 911S (Moton suspension, supercharged, etc) with Pirelle P-Zero Rossos (as it came new). Then, I got a set of Volk TE-37s in the same size but with Toyo R888s. I had both sets with me during the 4 days in a row that I was at VIR. I swapped them back and forth and back and forth. I couldn't get the heavier stock wheels and Pirellis within 7 and a half seconds of the time of my other setup. That is a huge difference fellas. Those are roughly two minute laps. Also, at VIR, it's kind of something everyone says by saying that roughly 75HP gets you another second, all else equal.