I think it's a great week to go! Maybe it's because we'll be there from April 21st to the 27th but everything I've looked at and heard say it's perfect. It's far enough away from Easter and Spring Break yet well before school starts to let out. I think historically it's one of the lightest times of year in terms of attendance and the weather is usually nice - ie not too hot. We went before during the 1st week of May and the crowds were great.
Good luck!