We were there the week before that in August 2007 and it was still pretty busy. Also, you're going over a weekend which tends to be busier than during the week. As I recall the parks started shutting down earlier during this time too (around 7 pm).
You can purchase an Express pass if you stay off-site that allows you one time FOTL per ride. For your dates its $25.99 for 1 park per day or $30.99 for 2 parks per day. If it were me I'd stay on-site rather than buy the express pass.
Another option would be to buy the 7 day unlimited ticket w/unlimited express pass offered on-line only for $259.99/pp. I don't know how many are in your party, but that might be a less expensive option for you.