OK, yes, you should run some numbers on the restaurants you are most interested in eating at to do some OOP vs. DDP comparisons. BUT when I read "
two teen boys," I think of my experience going with mine and feel like you need the DDP.
My teen meant no meal went unused, because if his youngest siblings split a meal (totally possible), he just ate a second meal. Yes, even with Disney portions. Any character meal or other buffet/AYCE situation is going to be a value for you to fill them up.
But sure, we did end up with unused snack credits, mostly because I made the mistake of focusing on the over-emphasized idea that "If it costs less than $5, it's not a good use of a snack credit." No. Keeping everyone fed, hydrated, and happy is a good use of a snack credit. We ended up buying candy and cookies to take home with the extra credits.
When we go this time, I am not going to hoard credits for fear of running out too soon. Kids will get all the sundaes, Mickey bars, crazy overpriced pretzels, and yeah, even Powerades if they want them. We plan to "Snack Around the World" at Epcot, possibly electing to convert QS credits into snacks if we run through our per diem allotment of 12 snack credits for our party of six.
In the past two years, Disney raised OOP food prices by a lot more than the meal plans, which only got back inflation bumps. People who felt it wasn't a good value in 2017 might find the math works differently in 2019.
Having said all that, though, I still find myself yelling: Never convert a TS credit for snacks.
That's the important question. If you don't think you'll eat all the TS meals, then the math won't work out at all--but there is the QS plan to consider if you guys don't do a lot of full-service meals.
Sidenote: The book "Dollars and Sense" covers the ways and reasons paying for an all inclusive feels better and leads to a better experience (meaning, is more fun) than paying a la carte. Which is not to say that the authors recommend it in all situations. But it helped clarify for me some of what I enjoy about the DDP. Paying for anything is literally painful, i.e. lights up the same region of the brain as if I socked you one. Separating paying and consumption reduces the pain of paying and increases the pleasure of consuming, which could be an unintended? bonus effect of having to pay off your vacation package in full a month before your trip. (Again, the authors point out lots of daily financial decisions that you *want* to be painful to help you make better budget decisions. They just also give a big example of how a big, infrequent vacation may not be that type of situation.) Making decisions is in itself taxing to the brain. So a plan that is already paid for and tells you it's fine to let each and every person in your party enjoy two snacks, to let everyone enjoy a specialty drink (my kids are going to have a lot of milkshakes and smoothies this time! DH and I are going to have our first Disney alcoholic drinks!) because it's all included, all taken care of, frees one from math, budgeting, and making some types of decisions as well as letting everyone indulge.
In short, "Did I save/lose money on the plan?" might not be the only meaningful metric.