I'm wondering - with the Nokian WR G4 tires, would I still need chains if I went up into the mountains? I sometimes go up to Frisco and Breckenridge, and I know conditions can be poor going through I70 into Summit County. Do snow or winter tires necessarily obviate the need for chains?
If you're set on having one tire for year round purposes and you plan on or might be driving during a snowstorm (i.e.: anywhere west of Denver) you should absolutely have chains both as a precaution and because on many roads there are chain/traction tire laws that go into effect and not having them would make you liable to getting a ticket at the least and an accident at worst. Snow tires are specifically designed to deal with colder temperatures and slippery surfaces such as ice and packed snow. Yes you can still break traction with a snow tire, but you and your occupants are all much safer because doing so is much more difficult with a snow tire than an all season tire.
Since you don't want to have two sets of tires due to storage, you should also realize that an all season tire will be a different and harder rubber compound instead of a softer, grippier rubber compound of a dedicated winter tire, which will directly effect your traction as temperatures drop below 30*F and when the road surface accumulates enough snow to pack into the abrasive top surface of pavement. The siping of the tire will also be different and generally designed for liquid water, which might not evacuate snow (particularly high moisture content snow) from the channels as well as intended during accumulating snow events which also compromises traction.
Studs are typically useful when snow has a tendency to pack into ice, or during an ice storm. They certainly do help, but they are only really necessary in more extreme cases. Not to mention they tear up asphalt and concrete surfaces faster, you pay more for them and typically by the end of winter you're missing a good amount of studs because the centripetal forces of the wheel spinning at higher speeds has thrown them into oblivion.
People are able to operate in winter environments with all season tires. Hell, every rental car/truck I've rented while traveling the globe with athletes as a Freeski coach for the past 10 years has come with all season tires. But usually they will be wise about the time and conditions they go out driving in, be very cautious when driving and leave extra space when following and braking because the all season tire will not bite into the snowy surfaces as well as a true snow tire, or they are spun around in 2' of snow in the median or one the side of the road.
I buy and use dedicated winters because I've spent a lot of time driving in wintery conditions growing up in VT and for work as I mentioned, and the cost vs. benefits equation made sense to me to do so. Not everyone is the same and really it boils down to what do you and your occupants feel most safe with and can I afford it. Storage is an easier problem to figure out, like hskrdu mentioned there are solutions you just have to be creative. Either way, have fun and be safe.
