I've read several threads here regarding second day free. I don't think that is exclusive to purchasing at the gate. Their website has alot of ticket information and you will also find info here.
I know we purchased advance tickets through a special I found here, on these boards, and paid $25 for each ticket. We ended up purchasing tix to SW and Busch Gardens for our entire family for $250. Drawback, they expire on 04/30/08. We bought them because our trip is planned for the end of April/beginning of May. We'll got to SW and BG first. . . . BG one full day and SW two days because we plan to upgrade SW tix to two days. I've read of folks who used those tix and got second day free, other folks who used those tix and had to pay a few dollars to upgrade to the second day. Unfortunately, those tix are no longer available, but my point is, check out all the information available to you and compare offers. You will get the best deal if you plan ahead, but if you purchase advance tix and then don't have time to go, you've wasted alot of money. You may also find offers, such as discount at the gate if you are a member of Southwest airlines (whatever was posted above), or
AAA or a variety of other "clubs". If you are going to Disney, you know it's all in the planning. My kids loved Seaworld and would actually prefer it to DW parks, but my kids are huge animal lovers. They love amusements parks too, but love to visit zoos, SW, BG, etc and actually prefer the more relaxed pace.
