A couple September opinions, starting with "lucky, lucky you."
First, Epcot still stays open until 9 PM for Illuminations. FW closes at 6, but Honey I Shrunk the Kids, Spaceship Earth, TT, and I THINK Universe of Energy stay open until 9. WS is open unti Illuminations. And on a Saturday, MK will stay open until 9, then have FITS. But I have to agree with dturner, MK is nuts on a Saturday, amazing since you have to hunt for people any other day.
We LOVE September. We've found despite decreased hours, the lack of a crowd means we can get more done on your average 8 hour day in September than a 14 hour day in July.
Our strategy last September: Pick a park a day (ANYTHING but MK on Saturday). On Saturday, we went to MK around 6:30, staked out a spot, and watched Spectro and FITS. All other nights, we went to Epcot and/or PI, usually both. Epcot at night in September is just a dream. Do ANYTHING you want.
Also, check out a waterpark on a Tuesday or Wednesday in September. You'll own the place.
In short, the lower hours in September are simply insignificant compared to the time and stress savings caused by no lines. Yeah, you loose some shows and parades, it's a trade-off. Personally, it's my favorite time. Hope it becomes yours!
Pat