Might be a repost but they have come out with a helmet that has a rear view mirror in it http://www.reevu.com/ http://www.youtube.com/watch?v=a9uLsMq7mBE
for the track? no. For the street, I can think of plenty of other brands I'd rather use. You already have mirrors on the street bike, why do you need another distraction in your field of view?