We just returned from our first Disney vacation. For us the Dining Plan was definitely worth the option. My advice would be to research your restaurant preferences and compare the Dining Plan price vs out of pocket.
For example, I would not use a Table Service Credit for Sci Fi. We dined there one day and opted to pay OOP. There are much better restaurants, IMO, to use for a table service. The atmosphere there is unique but I would compare the food to some of the counter service meals.
We also read many reviews, menus, etc for counter service options too because not every counter service is the same. You don't have to just eat "hamburgers & hot dogs" with the counter service meals. We enjoyed Wolfgang Puck Express and Tangeriene Cafe to be two of several good meals.
I do wish more restaurants had a better menu option for the children under 9. For example, at the Tangeriene Cafe my DSs would have opted for a smaller portion chicken or lamb entree instead of a hamburger or hot dog.
When we return to Disney we will opt for the dining plan.