I've always thought there were several legitimate reasons for using DDP. There is the obvious financial aspect of the plan, which most of us focus on. But there is also a convenience factor, and many people like having their food costs prepaid, before they get to WDW. There is also a hidden cost to DDP which is sometimes significant -- the increased room rate you have to pay to be eligible for DDP in most cases.
For us, the primary reason for using the plan was financial -- with 2A/1C, and given our normal dining habits at WDW, we saved an average of $75-100 per five-day trip. The elimination of the included gratuity wiped out that advantage for us, so we are no longer using the plan. Our decision was made easier by the fact that we always drive up to Disney, so we have a car and are not a captive audience dependent on Disney transportation. And, being DVC owners, we don't have any increased room cost because of using DDP.
However, even though the current plan actually costs about $10 more per adult per day for significantly less food, many families will find that it's still beneficial for them. The benefits of the plan depend greatly on a variety of factors, including some that have nothing to do with the DDP itself.
For example, if you are eligible for a better room rate, but can't take advantage of it because you would not be eligible for DDP -- that extra room cost is really a DDP cost to your family. That may be especially true if you are just as happy staying in a nice place offsite.
By the same logic, if you would normally fly in, DME, and use Disney transportation exclusively, renting a car to eat offsite would be a cost of NOT doing DDP that you'd have to factor in -- although eating offsite might still give you a significant savings.
You really have to look at the full picture, and make the decision that seems best for your family...remembering that there are non-financial benefits to DDP as well.
[ETA: In May, we're going for five nights. We're not getting DDP, and we're only planning to eat one meal onsite - a character dinner at Norway. We're going to be eating at least as well as we usually do onsite, including Charley's and Columbia, so we may actually spend more money, but get better value. We'll see.
I'll try to keep a reasonably accurate record of our food expenditures, and if it's accurate enough, I'll come back and post the results.]