I used to work at Universal (best...job...ever). Anyway, in August, every day is a crowded day, but at least you're going on a weekday. It will be hot as well. I would say go for it and buy the express pass which will get you into a separate line (that is usually short) on the side of the long, winding queue line. It's worth it if you don't want to wait an hour for an attraction that's only 2 minutes long. I recommend using your express pass for the new Simpsons ride that just opened, Terminator 2: 3D and other big attractions. If you like coasters, use it on the Mummy. If you like getting wet, use it on Jurassic Park.
Oh wait.....I just typed all of this and realized you're going to Orlando. Crap! Oh well, have a good time! And yes, get the pass. Nothing more icky than standing in hot, muggy, crowded lines.