Look at it this way maybe. If your car is towed to the track disregard this comment.
Your car is still a road car. If the spring are too hard, as will be the shocks. They will not do what they are meant to do. Which is to keep the tyre (the ONLY bit of the car in contact with the road) on the road. So it starts to become not so much an issue of 'whats proven and what might work on the track' but more so an issue of safty.
Say, a kid runs out on the road, your super stiff suspension is great until you hit the cats eye on the road, wheel comes OFF the road, you kill kid. (yes very extream example, probably wont happen just making a point). You cant then tell me, 'ahh well, it drifts better'.
Just something to think about.