Are you using a day of ticket media? Do you have hoppers? What time would you arrive?
It's absolutely 100% worth it if you are getting there for park open and can hop. Light morning crowds, leave when the party folks start arriving. Pick another day in your trip to start elsewhere (AK maybe) and get to MK for Happily Ever After.
It's less of a grand slam if you don't have hoppers, but it's still good day if you a) don't mind skipping fireworks or b) have a second MK day where you will see the fireworks. I like having a day in the middle of the trip where we call it early and get to bed at a reasonable hour.
If you aren't early risers, I'd say the value proposition is less because you get the most out of that low crowd level from 7:30 early entry to early afternoon. I wouldn't burn a day of ticket media if I weren't arriving before, say, 10am.