Let me give a revised suggestion:
2011: Check out the new Harry Potter stuff at Universal; it's amazing. (3 days)
2012: Check out the new Carsland, Mermaid, and Star Tours at DL/DCA (3 days)
2013: Check out WDW's new Fantasyland expansion (a week)
If you were to hit up Universal this year, I'd go in the fall, so you can add a few more days and hit up the Food and Wine Festival at EPCOT and maybe catch Mickey's Not So Scary Halloween Party. If you have kids that are teenagers, then I'd just opt to do the Universal Halloween stuff instead. I just wouldn't go during Christmas.