I had the same concerns and researched quite a bit on this topic. From what I have learnt, the all-season tires are crap in the winter and not that great in the summer. Also you want smaller, narrower wheels in the snow because they dig less into the snow.
The suggestion I recieved was consistant. It was to get 17" Rims with proper Winter tires for a non-staggered setup in the winter. So, thats what I intend doing.
Considering that I would be able to use the winter tires for 3-4 seasons, will (hopefully be able to sell the rims once I (eventually) get rid of the car, wont damage my nice Msport wheels by running them into potholes on the snow damaged roads and most importantly be safer. I feel it is worth spending the $2K or so for a dedicated winter setup.
2013 F30 335i MSport ED on Aug 27