Although I'm not a big fan of the
DDP (if I'm paying for it), since you stay Value I'd take the free DDP and go in September. Stay the extra couple of nights with your savings. Plan to be at the parks for opening, take a break midday when it's hottest, and head back to the parks in the evening. You might even consider using some of your TS credits for lunch to get a break from the heat. Plan to do the longer air-conditioned attractions when it's hottest out (3D movies, etc).
Room only discounts on Value resorts are generally only around 15.00 per night when they're offered. So, even if you were able to get one, that's not nearly the savings you'll realize with
free dining. I'd look at it this way, since you'll only be paying about 15.00 extra per night on your room (assuming you could have gotten a discount to begin with), once you've eaten more than 15.00 in food you're ahead each day.
If you don't want to do TS each night, don't. You're still getting a great value, no? How about booking Hoop De Doo Review or some other 2-credit meal? A night out with DH at a Signature Dining restaurant? Something you wouldn't normally budget for.
When we pay for the DDP we (meaning most of us) are constantly looking for the best value for our money...dinner instead of that character breakfast, for example. We went during free dining last year and it was great not worrying about what we were or weren't spending. It was only DS and I, so with just the two of us we didn't get as much 'free dining value' as a family of four, but it far exceeded the 15.00/night AP discount I gave up on our room. KWIM?