I wouldn't Count on Crowds dying down till at least Jan 7th..Many many schools are out till Jan 7th this year.Disney already extended hours after New Years in expectation of larger crowds
Last year I went from Christmas to New Years.. and the worst was on the 28th.. my birthday lol This year I will be checking in on the 28th and out on the 4th. I did it that way so I am still there for NYE, I can see the holiday decorations and shows at Universal and Disney, then also get some less crowded time before heading home on the 4th.