Yes, I ponder more "simple" Green answers while sitting on the throne, and my latest ideas happened right there! If you have more than one bathroom, I bet you favor one over the other because it clears in only one flush. Some require two or more. My favorite toilet was in a room with no windows, so I would spend time there reading with the lights on.
If I wanted to save water, I would favor the toilet that requires the fewest flushes. If I'd rather save electricity, I would use the toilet with a window that didn't need lights. Ideally, that bathroom would be the same room. If not, it might make sense to upgrade to a new water-saving toilet in the brightest bathroom.