Its a great time to go! We went mid September in 2004 and 2005. Very low crowds, thats after Labor Day so pretty much everybody is back in school. And too soon for Fall Breaks (for schools that even get them). In 2004 it was HOT, HOT, HOT! But we still had a great time. Last year, it was perfect weather. There will likely be a few things down for refurb since that is such an off time. But to me, the low crowds make up for it. Fireworks typically only run on Fri and Sat nites that time of year. Fantasmic is usually about the same. I think the 50th officially ends the end of September so it would be great to get a visit in before that ends. Another good thing about that time of year is the hotels both on and offsite offer great deals. Last year at Paradise Pier for instance we had a nightly average of around $128 a night with the stay 3 nights get one night free deal that the onsite properties were offering. Good luck with your planning!