I was jut there this past New Years we got there on the 30th, the crowds are going to be BAD. We did Epcot on the 30th and 31st, you couldn't move. We were there to do the last night of the Candle Light and New Years Eve in Epcot so we really didn't try to doing anything in the park, because it was so mobbed. On the 31st we went to DTD for Lunch and it was mobbed. On the 1st we went to MK got there about 1 left by 4 again mobbed.
Go with the plan you are there to enjo New Years Eve at Disney, you won't get anything done and your ride options will be limited , because of the long lines. I will keep going back for NYE because I love it, so the crowds don't bother me, I see it as it is better then sitting home.
The crowds will start to die down by the 3rd, but you will be gone by then, so enjoy what you can and don't let the crowds get you down.