it's been really worth it to go so early. We are night people, so enjoy the dark, so getting up early isn't much of a problem..........neither is staying up late. HOwever, afternoons are horrible for us. So, we'd always close a park, go sleep for 6 hours, get up and open a park, then after lunch, go back to hotel and sleep another 3 hours before going back to a park. We went when my older son was 4, 6, and then last year when he was 8 and our baby was 10 months. Never a problem getting our son up ........he hardly sleeps anyway, and the baby was easy!
Anyway, EE was the ONLY way to see Fantasyland in my opinion. Otherwise, you could spend a whole day waiting for those rides. We always rode dumbo and pooh twice, and everything else once with no more than 15 minutes wait. We've always gone at Spring Break or summer because I'm a teacher and can only go when school's out........so it's always pretty busy. EE was also the best way to ensure my son got his fill of the MOuntains, ToT and RnRC. I don't think we would've done any of these more than once without it. During Spring Break when he was 6 and 8, we rode each one 4 times in a row on the respective EE days with the most wait being about 30 minutes on the 4th ride of RnRC and Big Thunder. Right after the two big mountains on the one side of the park, we'd go over to Tomorrowland and do Buzz twice and then Space Mountain. By that time, we'd be waiting 35-45 minutes or so for Space. That would be one EE day and the other would be Fantasy land and then hop to Splash and Thunder. AK would always get rid of Safaris first, then do the raft ride..........but we don't want to do that so early this trip since it'll be colder. Those always built up big waits later. MGM we always caught the first Little Mermaid show after our RnRC and ToT...........we love the Mermaid! We found it was absolutely essential to do Test Track with EE as it just got way too long a line later, at Epcot. The rest seemed okay all morning.........but that was before Mission Space.
We are doing two things for the first time this trip: going at Christmas and taking a toddler. The biggest problem I see here is Christmas Eve and Day, and how to stay in a park all day since we may not get back in if we leave. We have PS for dinner both days, so really want to make sure we can keep them by staying in the park. It's at the end of our trip too, so who knows?
Good luck deciding what's best for you!
). 
We went right in and walked up a fairly deserted Main St. It was a great photo op with all the decorations and very few people around. DSs even got to see Buzz with no line as he was standing there alone too. The rides were all walk on, but of course the crowds grew as time went on.
