+30 mph you should be able to feel by the seat of your pants the results of aerodynamic treatments.
Aerodynamics Photos by kach22i | Photobucket
In your climate I suspect that you will be weary of going too low (snow) with the air dam and side skirts.
However the grill block could be a seasonal attraction, although I personally avoid such things.
Perhaps a smooth belly pan will weather a hard winter if installed correctly, but again it's your call.
