IMO, a rear locker provides a significant advantage any time you're trying to climb an obstacle, its chiefly a weight transfer thing I believe. The front tires just won't have the same weight on them, and consequently yield less traction.
I've had a lunchbox up front in my mini for more than a few years and eventually went to hydro assist because of it. I wheeled a couple years on semi loose or muddy terrain and loved it while as soon as I took a trip to Moab and got aired down on slickrock my steering said no more and just wouldn't cut it, cooking a power steering belt instead of turning. A noticeable understeer tendency is also a large factor, truck will just want to go straight instead of turning.
The front locker puts alot more stress on everything under there ie. hubs, birfs, shafts and ultimately the diff carrier itself.
The same truck of mine also has a rear lockright with over 100 000 miles of highway on it, I do plan to replace the unit eventually with a complete carrier unit like a Detroit in time, but its never given me any trouble, and consequently is a rather low priority. I happily put up with the slight increase in tire wear over an open diff for the off pavement capability and simplicity.
As far as snow and ice performance goes, I live in Canada, truck was my daily driver for many years, all year round. Yes the locker does have a tendancy to oversteer depending on throttle input, but I find it to be more consistent than an open diff, in that I can feel when I'm about to break traction, and its never a surprise to me.
Personally, I'd leave it just as it is, for the time being at least. Happy trails.
