Every weekend is more crowded than the weekdays no matter what time of year it is.
The first weekend of May (the 2nd and 3rd) is Bat's Day (goth day) and I believe there's going to be a convention going on with high school students over at the convention center. That will affect the crowds and make them larger than "normal" weekend crowds.
As for the second weekend of May, I'm not too sure what's going on.
We were going to go to the parks the first weekend of May for my birthday (the 1st), but because of the convention and Bat's Day we just moved our days to the week.
HTH!