the leaf isn't the draggiest thing in the world.
Fifth Place: Nissan Leaf
it would need about a 28% improvement to match the model S cda (claimed 14hp @ 70mph, vs 18 for the leaf), but the leaf is ~1200lbs lighter.
This user claims a %20 improvement from grill/mudflaps...
Details: Ruby - 2012 nissan leaf sl Fuel Economy - EcoModder.com
Aeromod nissan leaf improved aerodynamics increased range - My Nissan Leaf Forum