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!