We spent NYE 97-98 and 04-05 at MK. The park is packed. They usually do not let anyone in after about 11am due to the park being at capacity. We are "veterans" so since the rides aren't necessarily a priority for us, we ride early until the lines get long and then we shop, watch parades and people watch. The two times we have done this, it was the last day of our trip so the kids bought all their souveniers and since we weren't riding many rides, there's no problem with carrying them. This past time, we made ADRS and ate at LTT at about 4:30pm and when we were done, they had begun passing out horns and hats at several locations. We wandered around and saw them letting people on the Rose Garden lawn so we asked about it and it was for ABC's coverage. We signed releases and went in too. It was fun and a great view of the castle and Spectromagic parade but we were never on tv

It was actually nice that since they only let a certain number of people in there, it wasn't near as crowed as some of the park areas!
Anyway, all that to say, by all means go. Have a great time. Just have reasonable expectations. Make ADRs early and expect the most people you have ever seen in one place in your life!