Just my 2p's worth and not a dig at M3 owners in anyway...
I would push a 10k M3 with 4-5ks worth of mods MUCH harder than a 25 - 28k CSL round a track. Its not just the value - its getting another good CSL! You would have to spend days traveling all over, where as an M3 can be sourced much easier.
I was on KH at the same time as a lad in a 8k M3 with rock solid suspension and slicks and I could get no where near!!
It was my first time out in the car, but he was attacking corners like there was no tomorrow!
Oh, an it arrived on a trailer - I was driving home and going to work in it the next day
Stevie