If I were to lend my two bits although maybe not an option because of AWD but get an evo (preferably a IX). I just sold my evo. With full bolt ons they are easily 400awhp/400awtq and reliable all day long. 4G63 is a monster of an engine. For a dedicated track car they are cheap.
-Easy to make light 2900-3000lbs with basic weight removal
-Bolt ons are cheap and 400-500awhp is very easy on stock engine and has longevity.
-Already has Brembos, track pads are enough for most situations with 2pc rotors
-Handling and steering feel is second to none
-Tires are pretty cheap as 255/40/17 is pretty common size to track with
I owned a IX for 6yrs and ran it in all types of scenarios. Was FBO around 400whp with custom Ohlins, magnesium wheels, and sticky nittos. Weighed around 3100lbs and it was a beast at the track. My E92 pales in responsiveness and all out handling characteristics. Although the M3 is very very good the Evo was almost perfect. Steering and suspension feel with a properly setup evo with the amount of traction is almost cheating what you can get away with on the road course.
You can pick up Evo VIII's for around ~15k and IX's for around ~20k. It would be worth taking a peak. For a track toy I'd want something extremely reliable, easy to work on, and a plethora of aftermarket. My choices would be Evo IX, C5 Z06, E36 M3, or 350Z possibly.