Actually the crowds are higher late September-October Becuase of the F & W festival and MNSHP. They parks are still easily managed but there are more people.... Septmeber has still been low crowds with Free Dinning and even if ther is an increase in general the lines are shorter because people on FD spend more time eating and less time at the attractions. This has been my expereince.. The weather is great in OCT though.. the later the better.
Disney states:
The Lowest Attendance --
January (except New Year's Day) until just prior to Presidents' Week in February
The week following Labor Day until the week prior to Thanksgiving
The week following Thanksgiving until mid-December
More Moderate Attendance:
After Presidents' week in February through early March
Late April through early June (except Memorial Day weekend)
Columbus Day Weekend (October)
The first part of Thanksgiving week
Highest Attendance:
Presidents' week in February
Mid March through Late April ("Spring Break")
Memorial Day weekend
Mid June through Labor Day
Thanksgiving Day and weekend
Christmas week through New Year's Day