We did! That is the old SR3, then before deciding on Unity we were gonna use Irrlicht, it does most of the stuff like sound, graphics and physics but, every thing else has to made/coded by hand.
As much as I though Unity sucked combined with the fact it hasn't ever been used for a serious well known racing game ever before, I ended up being converted to the dark side.
Unity will do things for us with out sacrificing the game quality, or so I'm told. It's supposed to save time and labor.