Obviously, the answer to your question is going to be different for everyone. For our family, there is no downside to the DDP. For starters, we are still new to Disney. We've only been there once, so there is absolutely ZERO chance of boredom or monotony for us. That, combined with my type A personality and the need to plan our meals, and the DDP is a total win for us.
When we were planning our first trip, I really thought hard about the DDP. To make sure we would be "getting our money's worth", I looked through all of the restaurants and decided where we would most likely be getting ADRs. Then, I looked at the menus and figured out what meals we'd most likely get. I didn't just look at the most expensive because that's not really how we roll for stuff like that. I added everything up for our 10 day stay and compared the total with the price we would pay for the DDP. I had come within $50 of the DDP....and that was without factoring in the snacks.
I know some people don't like the DDP because of having to choose when they'll use their counter service meal.......do you use it for breakfast???.....or for lunch??...or do you use a table service for lunch and then use the counter service for a lighter dinner??...... For us, we wanted to get into the parks right at opening each day. So, I took instant oatmeal with us (in our suitcase) and we used the coffee maker in our room to make the hot water needed for the oatmeal. We had our routine figured out by the second day. The kids got up and got dressed while I made their oatmeals and then while they ate I made our hot water and got dressed. We were up and out the door in 45 minutes.
I used our table service meals as a time to rest and recharge each day. We never rushed and never bothered to look at he prices on the menu. That, right there, was the biggest pro for us. For us, having everything already paid for and just being able to pick whatever we felt like was totally worth the money. Now, I will say that we had 28 snack credits left the night before we left. I used those credits to by cookies (meh) and rice crispies treats (yum!!!) to take home for that post Disney Blues period you go through when you go home. We used some of those as souvenirs for friends and the LOVED them.
This time around, I'll still go through and do all the math like I did last time to see how the numbers play out. My kids will both be older than 10 this time, but I don't think we'll have an issue with hitting the numbers because my kids don't usually request "kids meals" type of meals. They'd prefer "real" food like steak, seafood, etc. We'll most likely ask them to try new things that we cannot get in restaurants where we live.
As far as not being able to eat your desserts........it was not uncommon for my kids to only eat half of their meals so they could eat the dessert (we were ok with that because we'd just get a box to take the remaining food to the resort to snack on our rest days AND we don't do desserts on a normal basis, so it was something special on our special trip) OR, we had the desserts boxed up to eat later in the evening. We did the second thing more often than the first and because of that, we didn't use the snack credits as much, but you already know how we handled the extra snack credits.
So, the answer to your question really does depend on how you family eats and how you handle things like that. If you aren't going to care if you don't get your money's worth and you have the ability to completely ignore the prices on the menu, then it's a great thing.
Oh....for what it's worth.... I saved every single receipt from meals on that trip and once we got home, I added everything up. Because we bought the DDP, we ended up saving about $300. Obviously, that won't be the same for everyone.