While I totally agree that the DxDP is the easiest plan to save on, in the sense you don't need to maximize every credit, its still become a lot harder.
Your $24 price point assumes using EVERY credit and every snack.
I find it difficult to use more than half the snacks on the DxDP, can only eat so much, so often.
So for me, the break even point is more like $27 per credit.
And surely, with appetizer and dessert, $27 is a very very easy number to hit at dinner. But if you use any of your credits for QS, you won't hit it. It can be pretty difficult to hit at TS breakfast. And even hitting that number at a TS lunch is no guarantee.
I realize it's only an average, so having some $20 meals can be balanced with some $40 meals, but I use some credits for qs breakfast, only getting about $9 in value ---- bringing down the average dramatically.
Did save on the last trip with DxDP, but most of that savings came from just a couple high priced meals.
I used the wrong number, it's ~$26.33. But still, that's a $2.33 difference, and not really that difficult to make up. And of course it assumes that you use every credit and snack, that's how the cost per credit estimates work. You are given those credits at the same rate, so they all cost the same. The value you receive for the credits is different and what comes into play if you spend them all or not. Ideally, you don't compare each and every meal with this number, but the totals at the end. This is due to the fluctuations that you mention.
And breakfasts tank every plan (except for kids at character meals).
I also dine where I want and and order whatever strikes my fancy without the DxDDP. If I'm full from my previous meal I can skip the starter or dessert. We have the Tables in Wonderland card and I would save the same $225 over your $1250 food value (20%). In addition, I get to enjoy any room discounts that may be available as well. For me, the TiW card is a better value since I am not locked into a dining plan.
As you know Cafeen, I was one of the originators of the "best bang for your buck" DDP spreadsheet. I know how much meals cost at WDW. As havoc315 points out, not all meals are priced the same and many breakfasts and lunches will not fall under your "$24 rule" unless you book buffets or the most expensive items. So, I think it's a little bit of a slight of hand when you say you only need to spend $24 per credit to break even. I think I would also quibble with you on the value you have placed on the refillable mug and the snacks. Right now you are saying that only $72 out of the $90 DxDDP cost is meals and the remaining $18 is 2 snacks and the mug. I have no doubt that many people make the DxDDP work for them and I could probably make it work for me for a couple of days until I was tired of running from one ADR to another stuffing myself and trying to fit park time in between my meals.
The question of if the DxDDP works for you in particular doesn't really come into play as far as what I was addressing. I was just pointing out that you don't need to order the Most Expensive Things at the Most Expensive Restaurants (METATMER) in order to
break even. Maximum value is different, and not something that anyone should strive to attain on a normal trip (if they want to try for a "let's see how much I can milk this plan" type of trip, that's different too

).
Now, I did use the wrong value above, either the 2011 one, or just one that randomly appeared in my head (see below for math for actual one). Still though, $2.33 doesn't make all that much of a difference (but boy, I've been using the wrong value for awhile now...)
And still, $26.33 is not difficult to attain at most meals considering the entitlements per meal, which is what makes DxDDP so easy (mathematically) to break even on. It's less "cost" per meal, with more potential value. (Note the "potential" there).
Let's take a look at The Plaza, generally a restaurant suggested as a good OOP value and not so good DDP value (we'll see how DxDDP affects it). We'll order mid-line, so not most expensive, but not the cheapest either. (Note: due to my tastes, I'd never get this meal

). How does a cup of soup, a grilled chicken sandwich, and some cheesecake sound? Don't forget the glass of lemonade either!
The total for this meal (before tax) comes to $24.96. After tax, this is $26.59. So, yes, it's on the edge for sure, but it's still above breaking even (at least, outside of peak times

) and it's pretty far from the most expensive items at the most expensive restaurants that many like to parrot. It's simply untrue.
Of course, as I also mentioned above, you can't really take a single meal in a vacuum. You really have to average them out across the length of your stay, but since a mid-level meal at one of the cheaper locations breaks evenly itself, then surely your average will at least break even while following the same mid-range choices at low to mid range TS locations, or even the low end choices at higher end TS locations.
Again though, if those meals don't work for you, and the number of meals don't work for you, then you aren't going to see good (or any) from the plan. That's how they work. They're designed so that you save money IF and (pretty much) only IF you're dining as they are designed. They have sharp falloffs for those who stray off the plans' structure (which is also designed, as a way for Disney to make money). It's really in all of our best interest to determine which works best for the situation rather than dismiss an option because it doesn't work for you.
For those interested
*The per credit math is as follows (see note above where I had initially used the wrong value) (We ignore the mug and use a $3 average for the snacks).
3Dx + 2S = DxDDP
3Dx + 2S = ~$85 (it's $85 and change in the slow season)
3Dx + 2(3) = ~$85
3Dx = ~$85 - 6 = ~$79
Dx = ~$79 / 3 = ~$26.33