Ate at both last June with DS then 8. While we were sitting in CG, he asks me, "Is this gourmet?"
IMO CG will give that more "gourmet" feeling. Narcoossee's is a very nice restaurant, but the navy table cloths, the loud wood floor, the atmosphere in general there is much, much more casual feeling than that at CG. If you are looking for a more "gourmet" feel, then I would opt for CG.
We enjoyed our meal at CG more than Narcoossee's. Also enjoyed our server. I think his name was David. He was AWESOME.
We didn't try for fireworks time. We went earlier in the evening. The restaurant was very quiet. Beware that if you do go earlier, the shades will be drawn. It will have a different feel to it. The view will not be as visible. If possible, I would try to time it so that you were there right before sunset. You can still see the view from the viewing balcony, the server will even suggest that you do this after ordering, or while looking at the menu (ours did). After the sun goes over the horizon, they lift the shades.
If you go earlier than fireworks, you can still go back to the restaurant later to view them, if you want. You keep your receipt and use that as admission back up the restaurant. There is a bar there, if you indulge, then you could get there earlier and have a cocktail and then go out to enjoy the view. David told us that the viewing balcony entered from the restroom side is a lot less crowded, FWIW, but we didn't opt to go back later, so I have no first hand experience there.