Thanks all for your replies! I have booked our short trip (3 days) and went ahead and just got G+ with the tickets so I don't have to stress about buying it each day. It looked like MK and DHS were sold out for reservations for the last two days of our trip based on the calendar, but when I went to book it (after buying tickets), it let me reserve those parks. Weird. I would have probably purchased a 4 day ticket, but our departure day showed only EPCOT for a starting park (opens at 11) and we have to leave for the airport at 11. So WDW missed out on our money for that day, as I would have bought a 4th park day if I could have for sure reserved a park that opened at 9am (any other park than EPCOT).