More often, it is ground clearance that will make the difference when traveling trails, not the 4wd.
We have 4wd and I find the low range more useful than the actual 4wd. I just put it in 4wd lo, but leave the hubs unlocked and Presto! 2wd lo range. Great for hooking up to a trailer, tight manuvering, etc.
Camburg makes a 2wd lift for vans that will go 90% of the places a 4wd will go, only it costs much less.