You both would need to buy the dining plan and if you are light eaters, it may not be beneficial to you to get the dining plan.
However, you need to remember that the MYW plus dining only covers 2 meals per day per person, so if you want to share 3 meals a day and maybe do a couple of signature restaurants or dinner shows, it still could work out to your advantage.
My advice would be to decide where you want to eat, what it would cost you (roughly) and then compare to the cost of the dining plan. Then you could decide if it was beneficial to the two of you.