I am part of the old guard, cycling with platform pedals and metal toeclips. It works fine all year round, except maybe if it were so cold I had to wear a pair of Sorel boots.
I cycle with city shoes that have a hard sole plus rubber overshoes (the civilian kind, not the cycling kind). I have a pair of wool socks with cut-off toes that I use as gaiters when it's below -20 C. I tend to have cold feet after 50-60 km only.
One potential problem I have heard with SPD is that the bracket may be a heatsink.
Regards,