Remember that the highs are not around for very long in a day. When we were there the week after Christmas we had some days with the highs in the mid 60's to lower 70's also. The mornings were quite cool and it didn't really start to warm up until almost noon. The high temp was reached at about 3:30 or 4:00, and the cool off started at about 4:30 and was very quick. If you're there early in the morning and plan to stay after dinner, you've got lots of hours with lower temps.
When we got to WDW in the winter I'm a huge fan of layers. We usually do short sleeved shirt, sweatshirt and jacket. For weather in the 60's and 70's, our family would be in long pants or capris. Hope that helps!