I've wondered the same thing, though we don't have ready access to a university like you do ;)
I would suggest including ones that add value to the courses you already have listed - e.g. Robert Pinsky for whatever English he did during the term when you heard him speak.
For the concerts, that would make a great FA credit - or 1/2 credit - particularly if you could add "listen to and discuss" the performances.
One other idea would be to include it in your counselor letter, just mentioning that you have done this over his high school years, what it meant to him, etc. There you could mention half a dozen or so specific concerts/lectures. :)