Thank you all for the encouragement and good advice. I feel much better. I do, in fact, have Nokian studded tires -- the skinniest ones available, with just a few studs. I've never slipped on ice with that bike and those tires; my fall last weekend was with my road bike and slicks, which was clearly a tactical error on my part. I guess I just don't know what's normal for riding in winter conditions, so I've just been doing my best. I have been meaning to ask, too, what you guys would do in the following situations:

1. Riding over a wooden (!) bridge in wet conditions or after it's snowed.
2. Riding over 5 steel plates in a row in wet conditions or after it's snowed.