I bought my Z4MC last October and managed to find a minter that had been garaged and protected from the elements. I had planned to sell my 320d immediately and use the zed, but couldn't bear the thought of putting such a clean car through snow, ice, salt, potential damage, parking dings (or more) at the station, etc etc. So I kept the 3 series through the winter and sold it afterwards, with the zed kept in the garage and only used on clear days. I put winter tyres on the 3 series, as it was truly appalling in the snow on 255/35/18 runflats.
By doing this I realised that having a daily car that I wasn't bothered about damaging (within reason!) was much more preferable than risking ruining a mint condition car. I've since bought an old X3 auto that I use as the daily bus, and like someone else posted, having an older, bigger auto 4x4 is strangely relaxing and should cost me bugger all in depreciation, and help maintain the zed in great condition - which makes me happy.
I'm surprised at some comments along the lines of 'just get out and drive the thing' even in the worst of the winter. I know it's a drivers car, that's why I bought it. But I wouldn't get much pleasure or excitement from nursing it through 6 inches of snow or on black ice.
Why use it if you don't want to or need to? Ownership pleasure comes in many ways, I'm sure many of us on here enjoy having a zed to drive on occasion and look after, and a daily driver that can do the trip to the tip, etc.