How exciting! I spent the fourth of july in Kauai two years ago, and there is a great fireworks show in Lihue. We didn't rent a car while there (we rented a condo in Princeville and got around on foot--a great way to see Kauai!) so we had to get a ride, but it was fun!
I have been asked which Hawaiian island the Poly is most like, and I would have to say Maui, because it seems laid back, friendly and relaxing. I might have to stay at the Poly to supplement my hawaiian addiction

. Right now, our next trip is planned for the Big Island, but not until Christmas! We are going to DL again in two months.
I wonder what the OP will decide?
By the way, to the poster who read the Frommer's article...Frommer publishes articles like that about just every tourist destination. It would be a mistake for a young family to visit Waikiki at the expense of Maui. The OP already knows what she likes! And one CANNOT get around the entire island of Oahu by foot...it is a huge island, in case you haven't been there. Waikiki yes, but that's a lot of walking and the most beautiful sights of Oahu are outside of Waikiki. If one went to Waikiki and did not rent a car, it would not be possible to see the north shore, Manoa, the lookout, Diamond Head, Sea Life park, etc. etc. The best parts of the island are outside the Waikiki area, IMHO.