Evening EMH at MK are the best! One of my favorite memories from WDW is doing MK at like 1am and just riding the rides that you would never probably waste time on during the day because of trying to maximize time in the park like the Carousel of Progress (sorry to anyone who likes that ride). My younger sister loved that ride, she was 11 at the time, and the song from that still makes me laugh at the memory of riding it with her, my younger brother, and mom at like midnight. We also rode the People Mover and did some other rides.
Morning EMH are a bit different for me because I try to be more productive and get to the headliner rides before the crowds. I try to do rope drop but I'm always there about 10 minutes after rope drop, I've only rope dropped once and that was for Pandora. I always have park hopper tickets so to me doing EMH is a must do. The park may get crowded later in the day because of all the people coming for EMH that remain in the park.
I think that if you have a park hopper then there is nothing to lose from trying out the morning EMH if you are already a morning person. My kids wake up early anyway and so do I and DH so we might as well be at the park. If you don't have a park hopper or you are staying off site, then I would say avoiding those parks might be a good idea. I'm not sure how the addition of Disney Springs hotels will do to the EMH crowds. My guess is that most people will not take advantage of the morning EMH. Most people don't rope drop either so going to the park early regardless of EMH makes for a few hours of comfortable touring.