I have done a lot of mods to my M3 and other cars. I have a new attitude towards the first mod to do on this car. Today my '97 M3/4 had the UUC Short Shifter installed and it changes the character of the car dramatically. I have done exhaust, intake, software, a/f meter, throttle body, underdrive pully, springs, shocks, and 18" wheels and I would say that the first and best bang for the buck mod to do is the short shift kit for this car.
It feels like the car went on a diet and is now ready for battle. I did the tranny mounts also. All of this for less than $500 was the best investment that I have made yet in the car.
Just thought that I would pass on the word.