I was faced with your decision last year, but after honest internal assessment of the limitations due to my rigs weight, width and height along with looking hard at where I normally go and type of terrain I travel on and my comfort with "pushing" it, I decided to forgo the 4wd conversion at $20k and instead make most use of rigs positives. On east coast I think size of vehicle is more limiting than not having 4wd.
Standard rig is 2001 E-350 Super Duty 2wd dually, with limited slip and 3.63 gears. To set up for off-road I went with ActionVans 4.5" front lift with 2" rear block kit. Tires are Goodyear Duratrac 235/85/16. Also got from ActionVan Fox Shocks valved for rig, fox steering stabilizer and 2008 radius arms. Recently added custom Ujoint front bumper and 12k winch. I also carry recovery treads, tire chains, shovel and snatch rope. And to make sure I know what I am doing I took a 2 day one-on-one professional off-road driving course that spent a lot of time on self-recovery, picking lines, etc...
I have spoke to and read about several people with these rigs with similar setup that they report are great in snow and slippery terrain.
Since I don't look for trouble I think my rig and recovery gear will get me out of the type of jams I could get in....if not I can relax in comfort until help arrives...LOL
My two cents...