Those things are a PITA, one of mine fell off and I have no idea when or where, the other was hanging on by one fastener. They are a crappy design and I live in TX (no snow). I can't imagine those things hanging on with any kind of snow or slush.

 

one fell off of my car, the other i took off, i notice no difference in noise or stability at high speeds

 

I cut or removed my air flow diverters when I dropped my car. I'm sure it was to help with wind noise at HWY speeds more than anything. Hard to believe they would be effecting the aerodynamics of the car in any measurable form.

 

thanks for the answer!