We were there at that time too. The weekdays weren't bad at all, a little busier than normal for that time of year, but the lines moved really fast. We never stood in line for more than 10-15 minutes, and some rides had less than a 5 minute wait.
The weekends are busier and more crowded, but when aren't the weekends like that?!

And, even on Saturday (the first day we were there), we didn't have any problems waiting in long lines. (It was kind of weird because there were A LOT of people there, so the park looked very crowded, but the lines moved so fast that the crowds didn't really have a negative impact.)
On Sunday, we were at the park late that night and were able to watch the second showing of Fantasmic.......HARDLY ANYONE WAS THERE! IT WAS AWESOME!
Then Monday - Thurs it was much quieter at the parks. We got to ride everything multiple times without a problem, then we went back to the Paradise Pier every afternoon by 3:00pm to swim and relax. (It was VERY HOT while we were there, around 88-90 degrees!)
I think it's a great time to visit. Just be aware that many Arizona schools (and possibly others) are on fall break around that time.