I think people see (or don't see) value in the DDP for multiple reasons. We always get free dining (here in the UK it's usually available to us) so in a sense, we always get good value. We do tend to gravitate toward the more expensive choices though to maximize the plan.
I recently priced it all out based on our receipts for previous stays for a friend of ours who is staying at a value resort. (In the UK, we don't get free dining at values at all, we only get QSDP with Mods and regular DP with Deluxe) The price they would have to pay for the dining plan (UK Prices) would be recovered easily even without seeking out higher priced choices.
The problem is, some people wouldn't actually buy all the items they do on when on the DP if they were paying out of pocket. So for some people, they can eat for much less than the DP costs.
This is absolutely true, on both ends. There are lots of devout followers of the DDP(s) on this board, and there are lots of ardent detractors. Neither is truly right or wrong, except with how it applies to their own trip requirements.
Now, the math
is getting considerably harder, since the plan prices are rising faster than the food prices, thus creating smaller windows of savings (and making it more difficult to reach the savings threshold.) If you're still looking to order from the top half at the menu from the upper half (or so) of the price range (per credit), then chances are you'll come out at least breaking even.
Of course, for me, it's never about the "High Score." It's about balancing the increased cost by using a plan (because you can ALWAYS eat cheaper than any of the dining plans) vs the experiences and value gained by said plan. If I go in knowing that I'm spending more to be on this plan, but at the same time, knowing that I'm getting closer to my ideal dining wants and the ideal is cheaper with the plan than without, then I know that it's going to work.
Basically, if the difference between the increased cost in the plan ($x) and the value that I'd be getting from said plan ($y) makes sense ($y - $x), then it should work for that trip, otherwise, I'd be better off with another plan, or OOP.
For example, in 2012 my math worked out so that I estimated about a $450 increase in cost by using the DxDDP ($x), in turn, I'd be getting roughly $700 worth of value ($y), so the difference of $350 was worth it to me.
For 2013, it's working out just the opposite. For an estimated ~$500 increase in cost, I'd be getting ~$505 worth of value. So that $5 difference, which could easily be lost by a skipped dessert, much less a skipped meal, made it not worth it to me. Since the plan number was already padded with a few meals and entitlements that I was only picking because I was on the plan, the subjective weight of the prepayment (peace of mind since I'm horrible at saving money) and the added experiences didn't balance out in favor of the plans this year. (Note: DDP was worse, since I'm only doing a few QS in here, I'd not even break even).
So, really, it's all about the math and figuring out what's right for you. Not getting hung up on the "High Score" mentality of "I must save the absolute most I can, even if it doesn't fit my trip!" is very important (and often lost in discussion.)
Now I'm just rambling because I don't feel like working...
It wouldn't be accurate, but it's your vacation & your rules. 
Having kids 9 & under + eating at a lot of character meals is the most obvious way to see a savings with DDP. Otherwise, you really need to be creative to save anything.
