I think it depends on how much time you spend at your hotel. We have small children, so we spend alot of time at our hotel. We LOVE the Wilderness Lodge. I have heard many people make the comment that Deluxe Resorts are not worth the extra money. But I think it depends on what you want out of your hotel. For my family, it is worth the money. We love the theming, we love the nice restaurants (Whispering Canyon and Artist Point) and the nice bar, and the scenery is AMAZING. It is right on Bay Lake which is beautiful. We LOVE the easy access to MK and the Contemporary (for the monorail), and to Ft. Wilderness (for Hoop de doo and lots of other activities) by boat because we do not like the buses. We just love the "feeling" that we get when we are there....it is so peacful. If it were me, I would use the money to try out the Wilderness Lodge.
For us, a huge part of the enjoyment we get while vacationing at WDW comes from the little things that make Wilderness Lodge special to us....sitting on the balcony drinking coffee at sunrise overlooking baylake, taking walks around the resort and seeing tons of bunnies and birds, listening to the peacful music in the lobby or out by the pool, watching the Electric Water Pagent from the beach with sleepy kids in their jammies ,renting bikes and riding through the wooded trails, sitting by the huge firelace in the lobby, I could go on and on! And don't get me started on how wonderful the Christmas decorations are there! (I know you are going in September, but I had to throw that in)