Haven't been to US during that time but have been to Disney and crowds are pretty low. Someone let me know if I am mistaken but I think you should be fine at an offsite hotel.
If you are going for a full week however, you can get some good rates onsite!
From 12/11/11 to 12/18/11, the price is $153.30 a night. I do not know what kind of offsite prices you are getting, but we enjoy the perks of onsite no matter what time of the year it is! You also need to consider transportation to and from the offsite hotel. If you are flying down, this will most likely require a rental car. If you are staying onsite, you can get a shuttle or town car service (highly recommend fltours.com) and not have to worry about renting a car or paying for parking since you have the boats to take you to and from Citywalk and the parks.