This is going to depend on how you want to experience the food and wine festival.
If it's a major part of your trip and you want to do the special events, don't get the dining plan. The only thing included in the dining plan specific to the food and wine festival is that you can use snack credits at the World Showcase kiosks (for food items, possibly for nonalcoholic beverages, definitely not for alcoholic beverages).
If you are using for yourself only one snack credit per day, you'll get one taste of one item (and they're small), and if you want to try others you will need to either use more snack credits or pay for the tastes yourself. If you are staying 8 nights and have 8 snack credits to use, you could use them all in one day and have a pretty good amount of samples. By that time, you may not want a full dinner in a restaurant though.
So, if the food and wine festival is just something you want to try for a day or so and you're sticking to the food kiosks, you can work it into the dining plan in that way.