There's just something about the atmosphere of MK after dark that I absolutely love. Whenever we've done Evening EMH at Magic Kingdom it's been one of my very favourite things. We don't even have kids, just my husband and I. The park looks fantastic with all the lights and I'd say do it for sure - and plan a sleep-in day the next day. That being said if you have something early to do the next day it may make everyone grouchy, but if you can plan a late day the day following it's a no-brainer. Crowds won't be as bad as they are during the day as the parents of little ones usually stay away, but I'd try it out anyway and know that the crowds thin the closer you get to midnight.... and even if you jump in line at 11:58 for a ride they'll let you ride it even if the experience takes you past midnight.