I do one track day/HPDE every month and use my M3, which is also my DD. I feel like this car is the best available mix of both. The primary track mods are wheels/tires, brake pads, high temp fluid, and stainless steel lines. Though, I'm leaning towards a Recaro pole position and harness.
The big worry for these cars on track is the brakes and the fact that the power steering reservoir leaks all over the engine bay. While rldzhao has started a thread about the steering issue, I've yet to fine a long term fix.
2007 GT3 Clubsport w/CGT buckets in Scotland
2003 CSL, SG, Alcon BBK SOLD
2002 M5, SSII/Blk and bone stock. In storage back home in TX
2008 M3, AW/Blk 6MT, lots of track stuff SOLD