This is probarbly the most unpredictable racing scene, and that is what makes it fun, imo. I race clean on the nurb pretty much 70% of my circuit time, and it does get tedious and repetitive at times, when you can ancticpate which car/driver combo is likely to win (yes I'm lookin at you Ford GT, for the 540pp races), but dirty racing is far more volatile in its nature; you crash, spinout, get nudged, blocked, cornered + then those who can't handle the mechanics, rage and never return (I played a few dirty sti vs evo lobbys).
More importantly, its challenging, yet fun. For those saying its "dum", racing around a track nudging people, is no more "dum" than say sliding around a track, and yet drifting is a worldwide phenomena.
Remember its the enjoyment in driving that wins people.
In my opinion, of course.