For now the Deluxe Dining Plan is "worth it" for us. First of all, we do a lot of character meal/buffets so our kids can get face time with all the "big stars" without having to wait on line. We also have some Signature meals lined up so having all those credits that can be table service OR counter service is nice to have. Plus, our youngest won't be on the dining plan because she won't be 3 by the time we take our next trip. While we may have to pay for some of her meals out of pocket, more often than not she'll be able to eat off of our plates or her sister's. I've done the math and while it's a wash give or take a few bucks for my wife and I, the "savings" are with my oldest daughter. While she won't be eating a lot, those character meals & buffets are pricier for her than the 30-ish dollars per night to get her on the dining plan. Plus, the snacks aren't kid sized, a snack is a snack. So our plan is to be sparing and sharing with snacks, once in a while using them in place of a meal during days with Signature Dining. After that, if, like the last time we used Deluxe Dining, we wind up with an insane amount of snack credits left over, we will take some fresher snacks "to go" on the car ride home - fudge or cupcakes, stuff that's delicious but won't keep for long - and then any left over snacks will go to packaged snacks, like the crisped rice treats or chocolate chip cookies or pretzels, stuff we can have after we get home as we go through Disney withdrawal.
Now again, I have two small kids so we find this to be worth the money. I don't know if I'll feel the same way as the kids feel less of a need to see characters, or as they get more energy so we don't need the sort of down time a sit down meal provides. With two teenagers, your mileage may definitely vary in regards to ANY of the dining plans being "worth it." Which is a vague term that change definition per person.
The Quick Service Dining Plan - 2 counter service meals a day, plus 2 snacks and a refillable mug - is nearly 40 bucks a night. I'd figure an average quick service meal with a drink and dessert for anyone 10 and up would be about 15 bucks, snacks could be anywhere between 2 and I think 4.50, add tax...maybe you break even. It's more convenience than anything else.
Basic Dining Plan - 1 counter service meal (with dessert), 1 full service meal with dessert, no appetizer), 1 snack and a refillable mug - is about $59 per person per night. There, you COULD see some value, especially if you choose to eat at buffets or other fixed price meals, because dinners tend to run near 40 bucks a head. Factor in a counter service lunch and a snack, you could save a few bucks each day. Odds are less or no value if you use any credits - counter OR table - for breakfast, best value comes from a counter service lunch and a table service dinner, and Signature dining will also significantly skew any perceived savings. If you don't need that many desserts per day, it's also less of a Value.
Deluxe Dining - 3 meals a day, your choice of counter OR table service, lunches and dinners always include appetizer and desert, 2 snacks and a refillable mug - that's $104 per night. If you opt to do a lot (A LOT) of sit down meals, and if you're a major foodie, you'll see the potential for the plan to be worth it. Just as a for example, doing some mental math, a day where you have breakfast at Crystal Palace, use snacks for a light lunch, and then dinner at California Grill (Signature, 2 credits) just eyeballing average prices for appetizers, entrees and desserts, adding tax, you're at 108 bucks. Random meals at Kouzzina for breakfast, Liberty Tree Tavern for lunch, and Crystal Palace for dinner, plus snacks and tax, seems like it could be nearly $110. It's just a question of do you want to sit down for that many meals versus being on the go, and can your stomach handle that much food?
So pretty much an epic way of saying "you know you better than we do." Go to allears.net and check out the prices of meals at the restaurants you've already booked, and the restaurant you're considering. Factor in the tax for paying out of pocket (pretty sure tax is included in the cost of the dining plan), and you may get an idea of whether or not it's worth it for you and your family.
Personally, I wish the regular dining plan would get a little more flexible, offer people the choice of an appetizer OR dessert. I think you'd see more people go on it then, as couples would probably split one of each.