I'd like to add the anonymity of riding at night. In the daylight everyone checks out your garb or your bike or your ass or your whatnot and it becomes who you are and what you're riding, not just that you're on a bike for the sheer pleasure of riding. So the darkness strips away those pretensions and brings it back to the source - the joy of riding and being taken to a different place than you are right now.

I also like how it heightens your senses and trains you to rely on primitive senses like shades of darkness and the variety of sounds and the feel of earth/pavement beneath your wheels. Being able to tune back into those is a human pleasure that the rest of urban society will sadly never know.