Just to give you an example of using a TiW card on a longer trip...last summer we went to WDW for 10 nights...me, DH and our 2 sons (they were 3 and 5 at the time). I upgraded to the AP and got the TiW card, since our ADRs didn't match with any of the dining plans. This saved us a ton of money, and it was an added bonus that the discount also applied to alcoholic beverages, since we frequently like a drink with dinner when we are on vacation. Also I ordered an app as my entree on occasion, and no worries as to whether it would be covered by a dining plan credit. We just ordered what we wanted, got 20% off of everything, and saved a good amount of money.
When I added up all the food we bought (meals plus snacks...but not with alcohol included), plus the price of the upgrade to the AP (
DVC member price) plus the cost of the TiW card, we spent around $1650 total. If we had the deluxe dining plan, it would have cost us $1860 altogether, and we would have had tons of unused snack credits, and some unused meal credits. So we saved around $200 doing it this way, plus the added bonus of 20% off of alcohol and 10% off of purchases when we went shopping (AP holder discount).
I did the math again with the 2012 dining plan prices, and it looks like the AP and TiW card will cost much less, once again...even though I expect the prices in restaurants to go up before next summer, I still think the TiW card is a great way to do a longer trip. And with your kids being older than mine, you will be ordering adult menu items, like you said, and you will save even more money!