I switch back and forth between 31" and 33" tires a couple times a year because the 31s are my street tires and the 33s are my off-road tires. They are both 10.5" wide and I get better gas mileage with the 33" tires than with the 31" tires. The reason is; the gearing is set up for the 33" tires with 4.56 gears. When I run the 31" tires, the rpm is higher and it sucks more gas. The only time it gets better gas mileage with the 31" tires, as compared to the 33" tires, is when I am towing my race car. I can say though that when I ran the proper 4.10 gears with the 31" tires, I got better gas mileage than I do with the 4.56 gears and the 33 inch tires.
I do recalibrate my speedometer when I change tires. I have a Dakota Digital calibrator that electronically resets the input to the speedometer for any size tire I want to put on my truck.
My point is, larger tires can provide better mileage depending on how the vehicle is set up. Each vehicle and engine has an optimum final drive combination (which includes the diameter of the tire) for maximum gas mileage. You can also maximize acceleration by changing gears and tire size and that usually decreases gas mileage. A common conception about tires size is; larger diameter tires lower highway rpm to improve gas mileage. That can be true but you can also go too tall and get out of the efficient engine rpm and lower mpg. That is without taking rolling resistance/mass, vehicle height, etc. into consideration.
Just to stay on the subject, I like the looks of wide tires, but like the characteristics of narrower tires. 10.5/33" tires are not wide tires but I don't think they can be considered skinny tires either. I also believe some performance is reduce by going too narrow.