You need to review the restaurants covered on the dining plan. This information is available at the Disney World web site--click on dining plan. The only character meal that counts as 2 TS is Cinderella's Royal Table. THe other "character experiences" that count as 2 are the dinner shows (the luau and BBQ).
The others you listed--Cape May, O'hana, Crystal Palace, Garden Grill, Liberty tree, 1900 Park Fare, etc. count as one TS each.
My suggestion to the "is it worth it" is to look at the prices for the various restaurants. Most of the character dinners are $28 for adults (as of 12/05). That doesn't include tax or tip. Tax and tip would add about another $5. The
DDP is $38 including tax and tip. So, you are getting a counter service meal (cost 12-15) and a snack for about $5 total. Of course, that assumes that you eat at a character dinner. DDP for a child is $11, which is about the same price as a character meal.
You can easily go to more expensive table service restaurants...for prices, see the all ears website.
Each family eats differently, and only you can decide if it will be a savings for you. Most people save significantly on the plan. Other options--if you are not a big eater, you might choose to use a Counter Service credit for a breakfast and share this with husband (or whoever). You might do the same at lunch, using a "snack" credit to get an extra drink and splitting the meal. You may want to do some cereal in your room and buy milk at the resort shop.
On the other hand, my sis likes to go to a sit down breakfast and a sit down dinner--no snacks or counter service. For her family, the DDP doesn't fit their needs.
We find it is a significant savings IF we eat table service every night....I also like not having to worry about what my teen orders!