It really depends on your touring habits. Parks with EMH will be more crowded on those days than they will on others, because people will go there for the extra hours. The extra hours themselves will see shorter waits for the rides that are still open. But on a non-EMH day lines will likely be shorter throughout the day. If you plan on staying in the parks late, and highly value the rides that are open during EMH, then it may be worth it to you
I avoid EMH nights, because I have young kids who don't like thrill rides and generally don't make it past 10:00. So to me, I'd rather have the shorter lines throughout the day since the little bit of time I might spend in the park during EMH are of little value to me. I do however partake in early morning EMH, because we are early risers and the rides available in the morning are usually more of the kid-friendly variety (especially at MK).
So, if you sleep late and play late and want to ride Space Mountain a few times at 11:30, then EMH may be for you. Just be aware that at 4:00 as people come to that park in preparation for EMH, the lines may be slightly loner than normal.