Mike's song, and Bill's bit about black vs. white pegasuses, were worth the price of admission based on just those two.
Mike's song was special because it plays to a certain comedy theory I've heard Simpsons writers describe a few times. Basically you take a joke, and it's kinda funny at first. Then you keep it up, and it becomes tiresome and unfunny. But if the joke is just right, and you keep it up still longer, it becomes hilarious. The guys at The Simpsons said their best illustration of this is in the Cape Fear episode where Sideshow Bob keeps stepping on the rakes. I thought that Mike's song was a perfect illustration too.