If you get larger diameter wheels with the same tire diameter you loose sidewall width. It may not seem like a big deal but in an off road situation that sidewall is valuable, especially if you let some of the air out of the tires for traction on sand or loose surfaces. Also, there will be more metal which makes the wheels heavier. That equals reduced milage. Changing the diameter of the wheels, in my opinion, is pointless. There isn't anything to gain from it, only loss.
Regular highway tread patters are rated to about 60,000 miles where all-terrains are usually 20,000. The highway tread usually last longer and the all-terrains sometimes come up short. The all-terrain tread patter is more aggressive and will result in lower gas milage. So you get worse milage and more frequent tire replacements at a higher cost because, oh yeah, they cost more.
If you flip through the magazines you will find that tires that fit on larger wheel diameters cost more as well. So, the way I see it, there is absolutly nothing to gain and everything to loose from larger diameter wheels. Larger diameter tires, I don't think, will add as much weight. So , unless you have money to burn, stick with the stock wheels and a highway tread.
