I always challenge those who swear by it to do the math...HONESTLY...and not playing the "this is what the plan provide" game.
The only time we've ever done the dining plan is when it was "free" (twice for a kids play, stay dine deal and once with
free dining), so we've had plenty of trips OOP. When we of OOP, our trips are definitely less enjoyable because we are constantly keeping track of what everything costs. As far as planning a head, there have been several trip where I get to the parks and the menu prices are more than what I found online. That adds up with a large party.
Now that Disney allows sharing credits, the plans are more than going to pay off for us. We can order DxDP for one room and have 84 dining credits, 56 snack credits and 4 mugs for $1550. We plan on CRT ($417 OOP), Spirit of Aloha ($356 OOP for cat 3 or $402 OOP for cat 2), Chef Mickey's ($230 OOP) and Akershus breakfast ($270 OOP). That's $1273 to $1319 OOP or 48 dining credits used. So, for the $277 that we'd have left OOP, on the plan we'll get 36 more meal credits, 56 snack credits and 4 mugs.
Now, if we couldn't share, we would buy the regular DDP for both rooms at $1950. After our planned meals, we'd have $677 to $631 left OOP or 8 TS credits, 56 QS credits, 56 snacks and 8 mugs on the DDP. Last trip (2015 OOP) we spent an average of $150 for each TS non-character/non-buffet meal, $75 at each QS for 2 adult & 6 kids meals ($525 for 7 meals), our snacks averaged about $4 ($224) and the mugs are $17 ($136, although the youngest two really don't
need a mug). So doing the math, we'd still come out nearly $400 a head without sharing credits, since we'd pay over $1k OOP for the "extras" we'd get after our 6 scheduled meals.
Could we minimize those costs by making meals in one of our kitchens or bringing in snacks? Sure, we could and we have. But, my kids enjoy the Disney Food Porn thread as much as I do and we spend a good portion of our planning time discussing the great meal and snack options, so our trips are definitely less enjoyable that way.
ETA: I did the math above with 2 adults and 6 kids since I was comparing to our 2014 costs during which my two oldest ordered off the kids menus since we were OOP (no character meals/buffets for us when OOP). Our plan costs will be a little more with the DDP for both rooms since they would be Disney adults on the plan, but our OOP costs will be too, so I think the math still sticks for that plan. The math is still the same for the DxDP room since 1A/3C will be registered to that room.