>In over 15 years of daily commuting (yes, all through the winter, too) I've been hit a half dozen times.

I don't know anything about your situation, but with respect, this seems extremely high to me.

>the only rule I follow is that I am invisible when on two wheels.

The strategy that I take to counter this is to actively make myself visible. Not only with lights but also with my actions.

If there is a tight squeeze coming up, I will take the centre of the lane and proactively block vehicles from passing dangerously if necessary. (The same if there are parked cars that may open their doors)

http://www.ctc.org.uk/blog/julie-rand/why-wont-cyclists-take... has more advice on taking a visible position.