On a track like MoSport, or a track where you can get up to a reasonably high speed, the aero (if you can make it light enough and tough enough so that it doesn't come off) could give you an extra few kph through a turn, which can make all the difference in the world if things are close. But if you do it wrong, it could hurt you as much as help...

Heh. I still remember the first day I took my 1G to 235kph. Passing through 190kph and the rear started feeling a little squirrelly. Then at 210 or so it just PLANTED it. That's when I thought, "So THAT'S what the rear lip spoiler does..."