I'm not sure what discount you're implying in connection with DVC. I assume most DVC owners are AP holders, since they get a discount on APs. And AP holders can purchase a card (Tables in Wonderland) for a discount at restaurants. I did this the one time I bought an annual pass. I paid about $60 for the card and it gave me 20% discount.
You can purchase the dining plan when renting DVC points. We've rented points 3 different times at WDW and always buy the
DDP. I like not having to worry about the entree cost - just get what I want. AND, since you're going in March, that might be one of the times of year when Disney imposes the "holiday pricing" for its buffets and all-you-can-eat restaurants. If you have DDP, you don't have to pay the upcharge to eat at those places.
Of course, I liked the DDP even better when it still included an appetizer and the gratuity, but I still think it's a good deal.
Hope this helps!