If you do not get one of the earliest reservations, you will not be able to have an enjoyable breakfast, meet the characters AND beat everyone to the rope drop. However, I think it's worth it. It's a total experience, the setting is magical, the food is surprisingly excellent, and it's far better than waiting in front of the Magic Kingdom gates and then rushing to your preferred attraction. if you can afford it, then absolutely you should do it.
Conversely, the food and the setting in the Animal Kingdom for that breakfast is dreary, plus it's still not very close to any of the top attractions when you are finished.