I've had my 2001 since new. I've tracked it at Mosport, Shannonville, dunville and toronto motorsports park. I'm not quite sure how many km i put on total between all those tracks but one time at mosport i did 320km in a day, it was awesome. The M3 is a great track car. All of my mods were focused on suspension and braking...spherical bearings, sway bars, coilovers, bbk with track pads and better fluid, R6 hoosiers with light weight wheels and harnesses. With all that stuff the car is seriously fun and extremely capable in my opinion. Could the car use more power? Sure, but as usual most people are really good at the straights but it is the corners that slow people way down. After 11 years of ownership i felt the car needed some more excitement and decided to put a turbo on it, HPF stage 2. I have not driven the car with the kit but i'm sure it will be fun and fast. One really important thing you will need to address with the E46 M3 chassis is all the weak spots to prevent failure. I've torn up my rear floor (needed replacing) and both front strut towers. At the end of the day tracking cost money and every so often really big failures happen and it sucks. Superchargers do heat soak after X amount of time and turbos have their own issues in the heat department.
I say turbo
2001 M3 - Phoenix Yellow - 03/01 production