Whether it's "free" or not, I can tell you it is a HUGE savings for our family of four that includes two teenage boys! There's no way any room discount is going to come close to saving me enough to feed everybody! Even paying for the upgrade to regular DDP instead of QSDP is a major savings, since a TS meal every day is a key part of our vacation.
Everyone needs to do the math for their own situation. But I'm amazed at how many people scoff at those of us using the free dining, as if we're being taken advantage of. I challenge anybody out there to find me a deal that's better for a family of four adults, who have at least 1 TS a day, and want to add park hopper anyway. Please, please...if you can come up with math that works better for our situation, I'd love to hear it!