I guess I've become a little soft in my old age. I commuted for years in my CJ-5 with a bikini top and soft doors, and I only had issues when it got in the single digits or lower. Block and inline heaters only worked so well on the 4.2L, and it took a long time to get warmed up. It also likes to swim a little in the ruts (short wheelbase, wider tires), which can get interesting on icy roads at moderate speed.
I've found that my AWD cars have been vastly superior in the conditions I regularly see. I bought a XJ Cherokee for $200 as a winter car one year, and never looked back. Even that beater rig was more suited to travel in the snow than my trail-oriented rig, and it allowed me to fix my trail rig at my leisure during the week- vastly improving the quality of my repairs and maintenance when compared to my marathon Sunday wrenching sessions.
Let's put this in perspective- are you talking about getting a well-maintained, partially/fully-restored Series III or a project truck? How mechanically inclined are you? How much experience do you have living in snow country? What kind of facilities (heated garage is nice) and tools do you have to work on a vehicle? A lot of questions like that will determine if it's a good idea.
I still say keep the Subaru and then buy the Rover as finances permit. That would give you a reliable backup in case it doesn't work out, and if it turns out you never drive the Subaru you can always sell it. Good Subarus sell like hotcakes in snow country, providing ample funds for the Rover project. And yes, it will be a project.