If your aim is the rides/attractions, it's probably not worth it. You'll find long lines for just about everything. If you will be more focused on parades, fireworks, shows, decorations and the general atmosphere and don't care if/how many rides you get on, then you'll find it well worth the time & expense.
Best wishes -
P.S. Since you are traveling with a 2 year old, I think another, less -crowded time will be more enjoyable for all of you.