My husband and I just returned from Le Taha'a (and 2 other resorts) and had several conversations about whether the meal plan is worth it. The MAP is breakfast and dinner. Full board is 3 meals a day.
Breakfast is a huge buffet with an amazing selection each day (and if you go to breakfast on the late side and are creative a little cheese, fruit and bread in the room goes a long way toward a light lunch!
Dinners are generally 3 courses on the meal plan but if you don't eat that much, it might be less expensive for you to order a la carte off the menu. You can look at the Le Taha'a website for menus (and I think prices for items if you order a la carte) at their restaurants. Additionally, the meal plan prices are listed on the price list.
One thing I will say about the meal plan, if you prepay (we did this for 1/2 of the days we were there--you don't have to take the meal plan every day), it is taxed at a lower rate than other services. Also, you can always decide to add the meal plan once you arrive.
Additionally, at Ohiri (the upscale restaurant) they charge you a supplement on top of the meal plan of $60 CFP. So the bottom line is for you to think about how large of a meal do you usually eat, especially at dinner where 3 courses are included in the meal plan. Hope this is helpful.