Great list Vik! One thing to add that keeps me going is riding with people younger/better than me. Trying to keep up (and sometimes even stay ahead) is a great motivator and has definitely made me a faster/better rider. I introduced a lot of my crew to mountain biking, and it's very satisfying to see them excel at it.
Great article Cam, and one I can relate to at almost 59. I especially like the bit about riding smarter as you age.