lots of stuff to consider.
-e85 only has about 87000 btu/gallon, which is quite a bit less than "pure" gas (114000). do some math and come up with what e10 has. still more than e85.
-you can make up for it being wimpier with the high octane rating which allows higher compression engines.
-but, your mpg will still suffer because e85 requires a lower air/fuel ratio. "pure" gas needs 14.7:1 at sea level. e10 is more like 14.1:1 iirc, and e85 is around 11.1:1, so your eating a lot more fuel for the same amount of air.
i think most people would spend extra money because the price is not low enough to compensate for the loss in mpg.