When we don't want to burn fossil fuel, and turn to Nuke, we end up having radioactive waste that can last very very long time.
Waste that is relatively tiny in volume compared to that generated by fossil fuel burning power plants while at the same time being far far easier to contain. Oh, then there's the potential for the 'waste' to be used again. I'm sure there's also a reliability argument to be made against 'renewables' as well.
I agree with you on efficiency. Using less to get the same effect is never going to be a bad thing. However, efficiency alone will not solve our problems. Coal/oil/gas is still being burned to produce the electricity whether you use it or not.
By the way, about the cars, when did cars in the US start getting so much bigger than in other places?