It can be "worth it," in the sense that you might save a few hundred dollars off of your food costs. It is not, however, as the OP noted, equivalent to getting dining for "free" -- it's just a discount.
When we visited last year during a "free dining" promotion, we'd booked a standard room at CBR (6 nights) with Magic Your Way (non-hopper) tickets. To get "free" dining, we had to upgrade to a preferred room (at a cost of nearly $400) and to parkhopper tickets (another $400, as there were 5 of us - 4 adults and 1 child). After our $800 in upgrades, we "saved" about $700 off of the cost of the DDP (which would have been about $1,500 for our party).
However, we also have to take into account that the cost of the DDP was already about $300 more than we were planning to pay, out-of-pocket, for what we typically order and eat at the restaurants we'd chosen (which mirrored the DDP in the sense that it averaged out to 1CS, 1TS, and 1 snack pp/pd - we just can't eat all of the extra desserts, fountain beverages, or snack substitutions that the DDP offers and is priced to account for). So at the end of the day, 5 people saved a grand total of about $400 (about $80 per person, or $13 per person per night) by making the changes necessary to secure "free" dining, and also received some minor intangible benefits from having a preferred room location and parkhoppers.
Granted, saving $400 is certainly better than saving nothing, and we were grateful to have it, but it's worth it to do the math whenever discounts are released, to see which ones are really better for you when all is said and done.