It seams pretty simple to me, if you give your tickets away for very little charge then you are walking down a very slippery road. Not only is it difficult to raise the prices back to "normal", think of the effect this has on group sales. I could be mistaken but I am pretty sure group sales are the bread and butter of most parks bottom line and you will have to cut way deep into those numbers too. If you cut your gate price for regular guests then you have to cut it even further for group sales for them to remain happy.
The law of supply and demand is pretty simple, lower your price and demand increases, so yes attendance will be up. But guess what, costs will be up too. I doubt the increase in attendance will offset the additional cost.
This is just a marketing ploy to get people to the park and it could easily backfire. I don't think it's genius at all, I think they are scared out of there minds (like Six Flags is) and are pulling out all the stops.