I think it depends on:
Who is in your party? Kids? Babies? Seniors?
How many times have you visited WDW?
If this is your first time, how likely are you to visit again in a year or so?
How many days are you going to be at WDW?
In general, I think EMH is worth it if there is an attraction or two that you really want to be able to see/do a couple of times. We generally do EMH every other day, and try not to stay out too late the night before or everyone is dead and wants to blow it off!