We run full winter tyres on our van in the winter. They're awesome! Our under-powered 9-seater minibus will make it up virtually anything with them on. It's embarassed quite a few faux-by-faux's.
Our place is a little above the resort centre here and hence the road doesn't get as well maintained as the lower roads do. Late Feb/early March often brings 3" thick boiler-plate ice on the road and we can still make it up without the need for chains. Summer tyres would see us putting on the chains every time we took the van out, and that's a real pain in the ar$e.
I think I put chains on twice during the whole of last winter, both of them down to having to stop/re-start on a steep bit due to other road users (i.e. muppets wandering around in a dream with skis on their shoulders taking up the whole road! 
).
We don't bother with a spare set of rims, they just get swapped on and off the standard rims and we store the summer tyres out of the way. Some garages/tyre places around here will store your "other" set of tyres for you for a small fee.
If you think it's going to be an issue for you, don't hesitate, get winter tyres. They're great. Chains are an option of last resort. They're a total pain and they break very easily.
NOTE: I live at 1,600m in the French Alps, not in the Highlands!
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