You can include your meals at GWL either with your room rate (in an "inclusive" package, as you saw on the website, which also provides a selection of extra stuff like stuffed animals for the kids, mini golf, arcade tokens, etc.) or you can add on the meals only (no extra inclusions like tokens) when you check in. So if you get a really good room rate then the latter would probably be your best option.
If my memory serves me correctly, when we added on the dining last year at check in, it was $45 pp for each adult (can't remember the kids rate as our "kid" and his friend were both 15 then and paid the adult price). I think kids were about $20 but don't quote me on that.
The $45 per adult charge included one buffet breakfast at the Antler Shanty Grub, one quick-serve lunch (there's several places to choose from....the onsite Pizza Hut Express, the sandwich/salad place outside the waterpark, then the fast food station inside the waterpark that sells burgers, chicken fingers, etc.), and a full buffet dinner at the Antler Shanty. The buffet lunch at the Antler Shanty refered to by the PP was not one of the lunch options as of last summer. Maybe that's changed for 2012.
If you are planning on eating all of your meals at the Lodge then you usually end up coming out ahead (which we like to do.....we enjoy the food very much, and quite honestly it isn't much different in price than dining at some of the other places around Niagara with the inflated tourist pricing......burgers platters and a pop x 4 people plus tax and tip once cost us $100 at Perkins by the Falls

) . When comparing costs, the meal plan you purchase at check in includes a drink for each person where the individually-purchased buffet price does not (it would be extra).
It certainly maximizes your time in the waterpark if you are not running around town looking for an alternative place to eat. The value of the breakfast buffet is around $16 or so pp, a quick service lunch will run you about $9, then the dinner buffet is
at least $20. So there's your $45. Plus then add on drinks for breakfast and dinner. Its nice to cover your meal costs at check in and then not have to worry about paying when you want to go eat.