J.R.
I don't know of any discounts but we encountered the same thing with the price last summer. We were wanting to do a close and easy before school started back trip and found that the rates were outrageous, so we waited until the week after school started back and spent the weekend when it was significantly cheaper. It didn't make any difference to my kids when we went as long as they got the chance to go.
As far as feeling jipped by the check in times that another poster talked about, you are able to use the water park before you get in your room. I think you can start using the water park around 11 am or noon on the day you check in. We stopped at the Rainforest Cafe for lunch in the Grapevine Mills Mall and then went over and checked in, and our room was ready early. If your room is not ready though pack all of your swimsuits in a separate small bag and they have really nice restrooms/changing areas that you can get changed in so that you can enjoy the waterpark. Also as far as the day you check out, you can continue to enjoy the waterpark after you check out as long as you keep your wristbands. We checked out, took our bags to the car (still keeping a small bag out with clothes that we planned to change back into before we left), and then were able to enjoy the waterpark the rest of the day. It was fun, my kids LOVED IT and it was nice that I didn't have to worry about sunscreen, it being too hot or cold, or lugging towels and lifejackets etc (all are provided at no cost). My only advice would be go down first thing in the morning before you get breakfast and grab a table and chairs, they seemed to go really fast.