1) It's worth it because if I drove around in the X3 in the snow with summer or even all seasons, I'd be going around corners at 0.5mph and braking half a mile in advance just so I wouldn't lose control. Sure, you need to slow down no matter what in bad weather, but winter tires provide extra confidence.

I unexpectedly lost control and spun out completely a year ago making a normal right turn with just a small bit of slush at a normal speed, not intentionally trying to do anything silly, DSC on. If you think doing a 180 in the middle of an intersection is "acceptable", then by all means stay with summers.

2) The cost of a fender bender or repair is FAR more than a set of winter tires.

3) I have a front-drive Lexus with summer tires on year round. Getting moving in snow/ice is difficult, turning is harder, and stopping is impossible. ABS kicks in and you keep flying forwards past the stop sign with no reduction in speed at all. Needless to say, it stays garaged when frozen precip falls.