I've been from a midly modded track EP3 straight into an E46 M3 which I modified for track, then back to my current heavily modded EP3. I had the same bug you did!
The M3 is a lot less exciting if I'm honest. It's just not got the urgency of the Type-R, the mental, buzzy insanity. It's a bit more laid back when pushing hard. It does obviously challenge and reward you in other ways with it being RWD.
My best advice is if you do for an M3, buy one ready modded for track. Because (much like the car you're selling) - you can pick something up with track mods for a fraction of the cost of modifying a standard M3 yourself. Try and get something with BBK, sorted suspension and square wheel setup. All essentials. Bear in mind engine tuning is stupidly expensive on these.
Oh and SMG is an absolute must if you're taking it on track.