Having just gotten back, here are my thoughts on the kids club:
It is a nice amount of space dedicated just to kids and always fun stuff happening there. That said, my kids used it about half as much as I expected them to use it since it was all they ever talked about, but actually only went for the "big stuff" on their list (ie Goofy Giggle Gala, the Lab, etc).
Register your kid so at least they have the option of going...they can do the graduation at the end then and get the shirt.
I think the smaller ones need the club more than the bigger ones...we dined w/a little girl of 3 years of age who was sailing w/her grandparents and it was obvious she never was away from them....she wanted to be w/my kids and watched other kids most of the time. The grandparents refused to put her in club even when we talked about it so she spent the whole week being dragged around by these two adults....it seemed that she wanted to be w/other kids and would have probably benefited even from a little time in the club away from grandparents.