If you plan to eat almost entirely at the parks, the dining plan is cheaper. We just got back two weeks ago and I must admit, Disney food had gotten much better than it was our last trip in 2008. But be aware, if you get the dining plan, you will get fat. :)
Typical table service meals can easily run $30 or more per adult. Counter service meals can run on average $15 per adult.
Being an RVer, eating back at the camper is easier than others staying at the resorts. You can take plenty of food for meals with you when you leave home. Plus there are a few cheap options. The Giddyup and Go take-out meal at the Fort is $24. Eight pieces of fried chicken, mashed potatoes, mac-n-cheese, and corn bread. A pizza is around $15 I believe. So there are options.
Dining Plan is cheaper if you insist on eating entirely at the parks or resort restaurants. Paying as you go is cheaper in the end if you can eat back at the camper from time to time.