I recently asked a similar question on Reddit, though my question was broader to BMW in general. There's some good stuff in there. Don't forget about rear subframe reinforcement and rod bearings on the E46 M3 in addition to VANOS.
https://www.reddit.com/r/CarTrackDay...commendations/
Personally I'm looking to get a E46 330ci/330i for under 10k and have plenty left over to put in Spec E46 suspension components, address maintenance, and plenty of seat time.