"It would take four-fold increase in in efficiency just to get even with our current cost of generation for all other methods. "
And so what, its completely irrelevant. If you get a 4 fold increase in efficiency but it costs 8 time as much to make and run, then you are worse off. You need to reduce the unit cost to make the stuff economically viable, no more no less. So half as efficient at 1% of the cost and you would be more than good to go for example.
Low interest rates will also help, as then the up-front capital costs become easier to absorb, otherwise after about 25 years net present cost of fuel for a coal station is effectively zero, just like solar.
Oh, wind turbines are limited by the Betz Law, not by any considerations of friction, and again the price of energy has sfa. to do with the efficiency of the machine, ih has to do with how much it costs to buy, how much it costs to run, how long the machine will last, and how expensive it is to borrow money. (and how much it costs to get rid of the stuff afterwards, but I believe it is normal to ignore this when you look at nuclear :P, or just build an extra reactor or two to cover the disposal costs if you live in Britain! ).