Like many of the others have said, whether it is "worth it" depends entirely on your family and their dining preferences. There's a huge difference in pricing for kids vs. adults - so it depends too on your kids' ages and how much/what they like to eat. I can tell you about how we made our decision and it may or may not help you.
Both our kids are over 10 and have adult type eating habits. We did not base our decision on our "regular" restaurant buying habits either. We're very thrifty and rarely eat out and when we do we really watch our budget. This vacation for us is a splurge - big time. We've never had a family vacation and it's our intention to do what we want, eat what we want and not be concerned with the price.
We're big breakfast eaters, and enjoy nice restaurants, so the deluxe plan made the most sense for us. A lot of people aren't crazy about the deluxe plan because it does mean a lot of time in restaurants and not playing in the parks. This wasn't a concern for us - for us, the restaurants are part of the "playing!" The deluxe plan is $71.99 per person per night, so for us it's $1439.80. When I looked at making ADR's I checked the menus at each restaurant both to see what they offered and to see what the prices were. I selected items that we're highly likely order and added it all up, and included snacks we're likely to buy. The total came to almost $1800 if we do exactly what we want - so the plan looks like a good deal. We love that it's all already paid for (except tips.)
I guess we'll see in July how close the plan is to how "reality" happens

All I know right now is that we're beyond excited that we're taking our first vacation ever, we're staying someplace really nice and can eat at the type of restaurants we really, really enjoy.
So...would the dining plan be worth it to you? Who knows? Look at the restaurants you want to eat at, run the numbers and take into consideration whether you have to "cut corners" on your vacation and think about which aspects of the vacation are most important to you.
So...there's the opinion/experience of a total vacation/Disney newbie. Hope that helps and hope you have an awesome vacation!