Depends on WHEN you are visiting, ages of kids, personalities of kids etc..No express pass at busier times of year means LOTS of time in lines and less attractions done.
If you are going in Jan of 2015, it again depends on when. Crowds drop down after New year, but that is when the Large tour groups start to arrive and they are there throughout the month. That can make for longer queues if you happen to get in line at the same time as them . We found on our last Jan trip ( and we are going again in 3 weeks) that the express pass was worth it( we stay deluxe on site to get it as a perk) to avoid the tour groups entirely