I have not needed 4WD in the 7 years I have owned my Excursion, but it's just used for summertime RV hauling. We do venture down dirt forest service roads with it. My take on that is if I need 4WD on a certain road, I'm not going to drag my trailer down that road anyway. 4WD is great, but not a requirement in a used budget friendly vehicle for most people's camping needs.
As to towing mileage, it is pretty typical of any gas powered truck with the same weight. With our old 28' 6000 lb trailer, I got 8-9 MPG. With the current 32' 9000 lb trailer, it gets 7-8 MPG. New gas trucks might be slightly better, but not much. Mine has 4.30 gears, a definite plus for towing.