VERY well worth it! There is only 1 "sit down" meal per day and you can take it at any meal you choose or you can use two of them in one day. For example when our family went in November we had dinner in Cinderella's Castle. That meal used two of our "table service" credits for each of us. We had breakfast with Donald in Animal Kingdom (The Tuskar House) that used one of our "table service" credits.
One hint...take a box of quart size ziplock bags with you in your suitcase. The portion sizes are HUGE! Often times we would get two meals out of one quick service meal.
If you really want to see the value of the plan, go to the Disney World website and look at the menu prices for the various restaurants. You will see what a value it is!