We visited DLRP from 7th - 12th Sept. The weather was pretty hot for us (coming from Scotland - hahahaa!)
8th was approx 70 degrees
9th " " 75 degrees
10th " " 84 degrees
11th " " 88 degrees
12th " " 86 degrees
We hardly had a clould in the sky and never experienced a spot of rain!
When queueing we enjoyed the cool of the shade for a wee break believe it or not!
We didn't really feel it was too busy except the weekend was mobbed (the good weather prob didn't help!). During the week was great.....I think you need some folk buzzing around to give athmosphere!
The weekend - Sat we went to the Studios which was much quieter and the Sunday we had a day sightseeing in Paris , so avoided as much of the crowds as possible!
I would certainly go in September again no problem, but yes avoid the weekends if possible!
Hope this helps!