Does it look like my air dam is bending backwards at high speed? Do I need new ones, or is this normal?

 

Due to distance of the picture, it's a little hard to say. Even new, the air dams are made from a flexible (nylon-esqu.. what they are actually made from escapes me at the moment) plastic. To ensure it being rigid/hold its form at speed (ie: your pic) would require some backside reinforcement, be it metal, aluminium or plastic bracing.

 

If it is bending, you could make your own to correct it. We've made a couple out of rigid semitruck mud flaps and aluminum L-channel, and they are very ridgid. We've had them going for about 4 years now and they're holding up very good.