We do the "two sets of all seasons" on a 4WD that my wife drives. We live where most of her driving is on dry roads, even in winter -- but when it snows, it dumps a LOT. So you'll want good traction for that, and the 4WD + fresh all-seasons works fine. OTOH, for the amount of dry road driving (in 40*+ temps) that she does, she would kill a set of winter tires every single year, so that doesn't make sense.
I bought a second set of OEM wheels off craigslist for $100. She uses the fresh(est) set of all-seasons in winter, then swaps over to the more-worn-out set of tires for summer, until they are dead. Since we live somewhere that it barely rains in summer, this strategy lets us run down the old all-seasons to the wear bars. If we were using only one set of wheels, I wouldn't be comfortable going into winter with all-seasons at, say, 4/32" tread depth -- even though they have plenty of life left for summer use.
I do have a set of true winter tires for my car, because I drive a lot less than my wife does, so I'm not going to wear those out instantly. Those are also mounted on a craigslist set of used OEM wheels. My 3-season set for my car are "ultra high performance" all-seasons -- basically as close to summer as possible, but keeping just a touch of winter usability. This lets me wait to swap over to winter until late November (when it gets cold enough, and/or consistent snowfall is expected), and swap back to 3-season tires by mid-March (when daytime highs consistently hit 45*, and the snow dumps taper off). I can still drive on snow if needed, on my "all-seasons" -- just doing it carefully. If I used true "summer" tires, they're a lot more temperature sensitive, and scary in a fluke snowstorm in early autumn or late winter.
I've also seen many arguments for a true "summer" branded tire + "winter" tire, claiming that it's cheaper than running down one set of all-seasons. I don't think that's necessarily true. "Summer" performance tires cost considerably more than an all-season, and don't last that long. You do pay a penalty for that added performance, in $ and in treadlife. The tire manufacturers sell a lot more "all-season" tires than "summer," so there is more competition and more availability.
There is also a wide range of all-season tires available -- from "touring" passenger car cruising tires that'll run 80K miles on a gently driven Buick, to "high performance" or "ultra high performance" ones that'll perform in dry much better, but still not quite as sticky as a true "summer" tire.
Tradeoffs on all of this, as usual. YMMV.