The M3 is two cars in one, but to some extent you pay for the two cars. For the price of an M3 you can practically get a new 135 and a used Elise, and the Elise is much cheaper to operate on the track than an M3.
As much as I love my car and the fact that no other car does everything better, it makes more and more sense to me to have two cars: a less expensive DD and a light dedicated track car. The benefits would be not only lower costs of consumables, but also no more tire/wheel/brake pad swapping.
Another "solution" that I find very tempting would be an Ariel Atom and a beater DD.