Hi Paula,
This is a great question, thank you for sending it my way. As you probably read, I too have a two year old. We have used the dining plan in the past, but considering that gratuity is no longer included with table service meal, I doubt we would save any money using the dining plan in 2008.
Like you, we mainly stick with character buffets. If you use all of your table service credits for buffets, you don't save much money. Also, you automatically save money just by coming with a two year old. Not only does he get free admission to the park, but he gets to eat free at the buffets. If you go to a restaurant like The Garden Grill, they will give your son a complimentary meal that comes with a make-your-own cupcake for dessert.
Just as a FYI, now that my daughter is closer to three we were able to have a relatively calm dinner at the
Whispering Canyon Cafe and
'Ohana. Both of those restaurants have a theme and kid activities that take place during dinner. Even with the activities, my daughter started to get bored before dessert came.
I think the dining plan is perfect for families who are happy with a snack for breakfast (bagel or muffin), a counter service lunch, and a non-buffet table service dinner with dessert.
I hope that helps. Have a wonderful trip.