I am debating right now if I want to get the dining plan for my Dec. trip. It doesn't appear to actually save any money.
I am looking at the Goofy's 4 days of dining and if I add up the cost of the 2 Character meals, the vouchers and figure $10 for the non-character breakfast in the park (the max on those is usually $8-$10), the dining plan is saving me less than $1.
The advantage for me would be that the bulk of my meals would be purchased ahead of time, allowing for better budgeting. Controlling your budget is really the only advantage that I can see.