I don't blame you for wanting it all, but ultimately, I don't think it's possible to do EVERYTHING there is to do at Disney World in one trip.
Personally, I'd try to move up the Be Our Guest reservation. Use the website, and you can even try calling 407 WDW DINE as well. But if no earlier time opens up, I'd stick with the one you have. (We're not big fans of the food options at Magic Kingdom, overall. We're trying Be Our Guest for dinner one night on our trip this coming fall, and hope it lives up to the hype!) Ultimately, you'll be watching HalloWishes on your trip, which is pretty darn cool, from what I understand. So you'll be getting your fireworks fix another night. (Plus at EPCOT for Illuminations, maybe? Or Fantasmic! at Hollywood Studios?)
But then, for me, I'd rather have a sit-down meal I can enjoy, where my family and I can pause and regroup for the evening + rest of the trip.
If your family would rather do a quickie meal from a counter service place and have one more round of fireworks? Then that's what's right for you.
Are you park-hopping? If you're heading to Magic Kingdom on a party day, without party tix (so, no Wishes scheduled that night), you'll have to get out of the park by 7pm. If you're hopping to another park, great. If not... well, you could try to catch Wishes (or rather, HalloWishes, again) from outside the park. If you're feeling like treating yourselves, you could do dinner at California Grill at the Contemporary, and watch the fireworks from their viewing area. They pipe in the music, and it's pretty cool from there. Or you could hang out on the beach at Grand Floridian/Polynesian and watch from there. (We did this at Grand Floridian 2 1/2 years ago - they also piped in the music, and while it was kinda far off, it was still fun to watch.) You could also consider doing a fireworks cruise. We did the Pirates & Pals Fireworks Cruise on our last trip, and it was a blast. You'd have to be in the mood for some pirate-y humor, but watching the fireworks from a boat in the lagoon was a very cool experience. If money's no object, you could go all-out and do a private fireworks cruise. Too rich for my blood, but I've heard people say it's an amazing experience!
