From your intended use, and with 4wd, I think you need one set of all-season tires. If that doesn't feel good enough to you, add a pair of chains in the back for really dire situations. Cheap. Not overkill.
I drive an awd Subaru, so far I've had two sets of all-season tires (the stock Bridgestone Potenza RE... 72s I think, and now a set of Pirelli P-Zero Nero M/S) and I have had no trouble with snowy roads. I bought the Pirellis from Discount Tire, I walked in with the Tirerack.com price and asked them to match it. They did.
If you're really going to be doing a lot of snow driving, I hear Blizzaks are the bomb.
I think the ONLY reasons to get two sets of tires are if your winter is really extreme, or you want to totally rip up the asphalt in the summer with a high-performance summer tire. I don't think either of these describes your situation.