I've been riding for years by this exact logic. Granted, riding in dark winter weather isn't exactly fun. Headlights blind you along 2 lane highways, you'll hit things and holes you can't see, changing flat tires with fingers so cold you can't feel them is a drag, putting on cold soaking wet clothes for a long ride home can be a downer, and even with the brightest lights and reflective gear things can be dicey with the drivers.

The trick is to come to terms with your environment. Besides, you eventually can get used to anything and when the light and warmth returns, it will seem absolutely miraculous. Plus, you're doing great things for your health -- it can be fun to be an "old guy" when you can smoke a lot of the 20 somethings on long rides the following spring.

Be sure to reward yourself for riding in the slop. Ribeye tastes best when you earned it by riding over an hour in freezing cold temps into a 15 mph headwind. You don't need to feel guilty about buying that compact crank when you haven't been paying for gas, oil, maintenance, or parking for the past few months.

Besides, even with your 20 mile commute, I'll bet that driving won't even save you that much time (maybe 30 min each way max)