It depends on your objectives during extra magic hours. If you are expecting no crowds and very short wait times you will be dissapointed. This used to be the case years ago but with more and more guests staying onsite now, I have found that the wait times during evening extra magic hours don't start to lessen until the last half hour or so. They do however give you more time to tour the parks. Get their early for headliners take a break at somepoint in the day, and then if you need to EMH are there to finish up the stuff you didn't get to do during the day. Just my $.02.
One exception, recently on a fantasmic night at the studios I was able to get on Toy Stoy Mania in about 20 minutes despite the posted 50 min wait. But you are going to the Epcot and MK so this doesn't matter haha.