We will be attending the party that same day this year. I am not sure what the crowds will be like because the last time we attended it was the week prior to Christmas and it was a bit crowded.
I think that the party is worth it to my family but value is subjective. I think that you might want to check out what you get at the party. Is the parade, the supposed lower crowds, the extra shows and the fireworks etc worth the money to your family? While my family enjoyes it not every family will find the value the same. I missed the ages of your kids but look at that as well, this party does not start until 7PM and while you can get in to the MK around 4PM you are going to want to stay late. Does your family do well with later evenings? Can you avoid getting up early that morning r will they rest in the afternoon?
I will check back after we get back home and let you know what the crowds were like this year.