Rachel,
I am assuming you are talking about the Wishes Fireworks at the Magic Kingdom? Because if you mean IllumiNations at Epcot, I would not leave the park, but would instead try one of the many great World Showcase restaurants!
As for Magic Kingdom area restaurants that I would go to before returning for the fireworks, here are my favorites;
Fun for the kids
- Whispering Canyon Cafe
- 'Ohana
- Chef Mickey's
Fine Dining
- California Grill
- Narcoossee's
Other good choices
- Kona Cafe
- 1900 Park Fair
- The Wave
Now there are other choices, but some of them (like Spirit of Aloha and Hoop Dee Doo Review) are probably too much of a time commitment, and you can miss the fireworks depending on what seating you are attending.
Based on your question, I think that the first set of recommendations are probably what you are looking for, and I like all three for different reasons. Whispering Canyon has the best food, and a really fun atmosphere. 'Ohana has decent food, a nice atmosphere, and an incredible view. Chef Mickey's has great food variety, and is a great character experience.
Keep those questions coming!
Have a magical (and delicious) vacation!