I've never seen this information all in one place. Gay Days are generaly the first weekend og June, and the grad nights are, obviously, during grad season (They're closed events anyway, so they shouldn't really effect regular park attendance).
Magic Music Days and the cheerleading competitions happen year 'round, but in my opinion they don't add significantly to the crowds. The time of year is a much bigger factor. My wife and I saw a lot of cheerleaders in the parks last December, but the crowd levels were still typical for early December.
I did overhear some people saying that the cheerleaders were annoying, but I didn't observe them being disruptive in any way - just kids having a good time. Some people are annoyed very easily.