I use all seasons permanently on my works van. As you said yourself, they are a jack of all trades master of none. They are a good improvement over summers on mud or snow, but they'll only help so much. I've still managed to get the van stuck in places I didn't expect (that's when the snow chains come out). I often have to get my !Removed! heavy transit connect up gravel tracks, fields and generally poor roads. If I still had summers on, I would be walking a lot more.
If you're not doing much 'off roading' then I would recommend you stick to summers and just take extra care in the 1.5 days of snow we get. I bought a full set for my STi this year and I've hardly used them at all.