I vary the route somewhat, most recently due to road construction. Another good reason to vary the route, from a safety point of view, is to avoid getting you and a possibly expensive bike "cased", by shady people. This is not too big an issue with me since I ride a pretty "safe" area.

I also vary the way I ride a particular route. For example, there is one intersection where I turn left from the turn pocket, or go through the intersection and cross at the light from the other side. The is very much in keeping with your idea, since the decision of which way to do the turn is based on paying close attention to the conditions; If the through light is green, and the turn arrow is red, will the light to go through from the other side change first? If the left arrow will change first, is it safe to move over? (usually is)