Gerrie,
Certainly you have to decide if you want to do the meal plan or not before you get here, as you cannot add the meal plan after you arrive. It has to be added to your reservation three days or more before your scheduled arrival.
That being said, I think they are typically a great idea. What you can do is review the three main plans (Quick Service, Standard, and Deluxe) and get a feel for which best matches your particular eating habits. The
printable PDFs that I link to here are really helpful.
Assuming you find one that matches your dining habits, I think you will find that they are a great money saver. I have priced them out on several occasions, and every time I have found that it saved me money. The convenience is a nice feature as well.
If I can help you look into this option more, please feel free to ask me more questions with information on what you like/dislike in your dining.
Have a magical (and delicious) vacation!