Julie,
In most cases one dining plan or another is going to be a money saver for most groups. There are times or cases where it might not be, I am sure. But typically they are a great way to save. Most families seem to choose either the quick service or the standard plan. Mostly of the two, it is the standard plan. The deluxe is a great plan, but for families with smaller children they will find that that is more food, and more time in restaurants, than they really need or want.
First, decide what kind of dining you have in mind. Are you a counter service family? Do you like a sit down meal three times a day? Or do you do a bit of a combination of the two?
Next, I suggest you download the relevant plans from the
Disney website, and then get your travel agent to price out what adding these plans would cost.
Finally, compare those costs to what you expect to otherwise spend by looking at menus on AllEars.net. That should help you decide.
And send me any follow-up questions that you may have!
Have a magical (and delicious) vacation!