Though I can't speak from experience (yet!), I can tell you that we'll be going in the last week of August this year, and I've learned from countless posts on multiple boards that park attendance does drop off in mid-to-late August due to many souther schools (not just Florida!) starting back well before Labor Day.
I also can't speak for what the Fairytale Package promotion may do to increase attendance beginning in early July, but I can speculate that however busy the resort is in July and early August, it will (probably) be quite a bit less at the end of the month primarily due to schools starting back.
I hope that helped!
Jon