Depends on what you want it for.
Looking to save money? Then you have to plan and tailor your dining so that you save money on the plan. And it will depend on where and how your group prefers to eat, the makeup of your party, which dining plan you chooose, and whether you can get ADRs for the restaurants you want (if you select a plan with table service component). In general it is somewhat difficult to save money on the quick service plan at all, the best type of party for the regular plan (the one most guests purchase) is a group with several children under age 10 who plan on doing a lot of character meals or buffets/AYCE, and the best type of party for the deluxe plan would be those who want a signature dinner (2 dining credits per person) each night of their trip.
Do you just like the idea of a prepaid dining plan? Does it really matter to you whether you lose money on the deal or not, so long as you don't have to look at the prices on the menu? That's a value that you personally will put on having the plan.
Generally speaking, you'll only save money if you have multiple children ages 3-9.
If you define "worth it" as something other than saving money, you'll have to make that call based on your own judgement.
Is the dining plan worth purchasing ?
I disagree with this completely. We - a party of all adults - have done the regular DDP for years and we either save a bit or come out even. We do not have children 3 - 9 and we do not do any character meals. It suits our way of eating.
The only way to know for certain is to do the research and math yourself for your party. Look at the menus for where you will eat here on the DIS or at allears.net. Price what you are likely to order each and do the math. Compare that do the daily cost of the DDP and see whether you would save money or not. Remember tax and gratuity are not included in the menu prices and need to be paid on top of your assessment either way.
Good Luck.

You "completely" disagree with my "general" advice? Yes, it can work for some people. If you always drink soda with your meals, if you always eat dessert, and if you always order expensive entrees, you will save money. If not, the savings from the children's price is your only hope for coming out ahead financially.I disagree with this completely. We - a party of all adults - have done the regular DDP for years and we either save a bit or come out even. We do not have children 3 - 9 and we do not do any character meals. It suits our way of eating.
You "completely" disagree with my "general" advice? Yes, it can work for some people. If you always drink soda with your meals, if you always eat dessert, and if you always order expensive entrees, you will save money. If not, the savings from the children's price is your only hope for coming out ahead financially.