I have kept up my riding more this winter also. I'm in Ohio. I rode in to October with my regular SPD shoes. When temps were even in the 60's I started thinking about the "keeping feet warm" predicament. I ended up coming up with a way to put SPD cleats on aluminum plates strapped to a pair of winter boots. The boots I am using are Vasque Snowburban's. I originally got them for winter backpacking and snowshoeing. The SPD adapter plates are quite goofy looking, but truth be told - I have not wore any other shoes/boots riding since I made the adapters. They work absolutely fantastic for me. The best part - toasty roasty feet!
I have a pretty good system for layering clothes, face protection, and hand protection. However, keeping my feet comfortable has been the biggest challenge. The reason being - I can't ride much distance at all without being clipped in. I've overcome some pretty goofed up muscle/tendon issues that lead to knee problems - and the root of the problem was platform pedals. The muscles and tendons on the tops of my legs built up to where my kneecaps were stressed sideways and ground in to my leg bones. So by being able to pull my feet through the whole crank cycle I can work the opposite muscles/tendons at the same time as taking off a lot of the work on the tops.
In any event, I can keep warmer than I've ever been able to this year and that's kept me on the bike a lot more. I know I am not riding the mileage a lot of you do but any riding through the winter for me at all is a good thing.