From the following image we can determine that both mirrors make up 2% of the total frontal area. No matter how well those mirrors are designed, they at least add 2% to the aerodynamic drag. Plus, there is an unknown Cd penelaty associated with the form drag of the mirror itself.
Best case scenario probably is that the volt's mirrors halve the aero drag penality over your average side mirror.
Generaly side views mirrors make up 5% of the total drag of cars. You could as well say that any average side mirror would not impact the range of the volt as the difference will probably be witin a mile.
