I think the decorations for the most part are taken down within the first few days of January. The contempory's undecorated tree outside was still up at the end of January last year when we were there..
We go every January and we love it then. As long as its not Martin Luther King weekend, its dead at the parks.
As for weather, we have had it all from mid 80's all the way down to waking up to 28 'record breaking,Orlando schools are closed' degrees! The only good thing was that back home in Pittsburgh that morning, it was negative 13 and that was WITHOUT the wind chill!!!!! It was a chilly trip at night at in the mornings that year, but during the day we had on jeans and t shirts. I prefer a warm day, even cool where we have to wear a sweatshirt rather than sweat to death all day like we did last October. You just have to check the weather right up until the night before you leave and pack a little of everything. The first year we went, before my disboards, i packed jeans,sweatshirts, heavy coats..etc and we never needed ANY of it, it was so beautiful. The next year, I brought one pair of jeans and one sweatshirt, and the nights were chilly and we had to buy warmer clothes. This past January, it was awesome, but it was the first trip out of 8 that we had rain more than 2 minutes. I think it rained most of the day for 2 days.. blah.. Just keep your eye one the forecast and be prepared for anything. It really is a great time to go. Cheap time too!!