I just booked a 4-night stay here for my wife and 1.5 year old this coming September (9/11-9/15). We had 4 free night awards to burn and this seems like a good use. We'll probably mostly stay on property, but will maybe hop over to Animal Kingdom for an afternoon.
From everything I've been able to gather, the crowds do die down a bit after Labor Day. For anyone that has visited the hotel (and the parks) in mid-September, can you shed some light on what the crowds are like?