This makes rest of my statement even more true (lower resources costs -> cheaper electricity -> cheaper manufacturing of electric vehicles -> better business for Tesla).
All they need to do is keep being focused on their primary business, instead buying SolarCity.
Electricity is basically free compared to gasoline. If you cut the price of electricity in half, it wouldn't move the needle at all on EV sales.
Energy used for production of electric cars/batteries (or any other thing manufactured in modern factories) isn't made from gasoline...
It's significantly cheaper, but it is far from free (unless you are actually not paying for it). Even at a generous $0.10/kWh a Tesla costs about $0.029/mile. At $2.20/gallon, a 30MPG cat costs about $0.073/mile.