Spending a Disney vacation in September is the greatest. Perfect timing for lower wait times, crowds, air, resort, and car rental prices are lower too. Disney usually runs a free dining special (as they are now) for most days in September. My family and I have regularly booked the free dining offer for about 5 years now. Its the way to go! Yes, the normal park hours are some what shorter than they are in the summer, but if you stay at a Disney resort take advantage of the extra magic hours. The weather is still warm but not unnecessarily hot. With this in mind, make use of the water parks because they tend to be less crowded as well. Hope this helps!