I do think the 60th events will make the parks busier, but I don't know for how long after summer. I certainly expect to see a bump in the spring and summer crowds, but whether it'll continue into the fall and winter depends on what they do regarding Halloween and the Holidays. When you say "off-season", what do you mean specifically? I ask because December is kind of an odd month. The week of Thanksgiving is usually very busy and then it drops off. Crowds build up throughout the month of December, with very high crowds the week of Christmas and New Years. I've gone both the first and second week of December and there was a noticeable difference. The first week in December was pretty manageable, with not bad crowds on the weekdays. The second week was okay on the weekdays, but the crowds were pretty substantial on the weekend (Fri to Sun). So if you are thinking of going in December, I would aim for as early in the month as possible. Mid-November would also be a possibility because the Holiday decor should be up, but the crowds aren't really huge.