To the OP we're not long back from Hawaii where we spent most of our time in Maui, just a night or so in Waikkiki. One of the other posters is correct, Waikiki is a lot like Surfers Paradise not really my favourite and the hotels are quite pricey. A lot of the flights back to Australia (Jetstar for example) leave at about 8.30am in the morning so there's no choice but to overnight in Oahu the night before you fly. We flew this time with Jetstar. Paying for extra legroom seats in economy and the meals and entertainment package was money very well spent.
Maui
We rented a great condo in Lahaina just a few blocks back from Front Street..
Maui Paradise Rentals - Maui Vacation Rental Resort Information April who resides in Washington DC is a pleasure to deal with. We stayed in the 2BR condo. The grounds of the resort have great gardens, a pool and a lanai with seating like a queen size bed and a thatched roof overhead. An a BBQ. We'd go back here in a flash. We had a Chev Impala for our 5 days.
I wouldn't personally worry about Gerards in Lahaina either to eat or stay. This condo is far nicer, has included high speed wifi, all the good USA cable stations. Main Street Lahaina is fabulous, 1915 type architecture, America does simply the best burgers and the Mai Tais in Lahaina were far better than on the North coast. To my mind I could happily base myself in Lahaina and 10 miles north or south of there. There's a particularly nice bakery and bit of coast 10 miles south Lahaina.
On Maui we also spent a couple of nights in Paia in a hotel that gets rave reviews online. The Paia Inn is hideously expensive, no breakfast included and parking is in paid lot down the street. The whole of Paia has a hippy vibe, that and hippy type food is not my go. With the Hana Highway we did that one afternoon. Hana when you get there is nothing special. But if you continue on through Hana south to do a bit loop back to Paia the road gets interesting. Very interesting and remote. We had this Chev which luckily was solid with high profile tyres. The road is narrow, mostly bitumen. It's possibly like the east cost of the North Island north of Gisborne. Up where they filmed "Whale Rider". That part of NZ few white people go. South of Hana has this wonderful remote feel to it and once you get to the other end some interesting hotels and bars. Yes you can leave Paia late morning and be back about 8pm at night. But a nights break in Hana might be a decent idea.
Kauai
The northern end of this island is fabulous. Green and lush, around Princeton is fabulous
Big Island Hawaii
Really liked the feel of this island. It's quieter than the main island. Kona is pretty decent.
Oahu
I don't really like Waikki or to be honest a lot of the tourist norms in Hawaii. Hawwain Airlines staff just stand back as you self check in your luggage. I would have thought in a country where there's a short of work, low wages, that there would be people around to load bags, etc even if you had to tip. But no. Gas and groceries is expensive in Maui. America and Americans seem forced to queque for everything.
The rental car lots are generally offsite to the airport. And hotels in Waikkiki in Jul are very expensive. Condos charge you a cleaning fee of about $150 when staying at Maui. The food at any USA airport is awful and they are a bit of a nightmare to negotiate.
But the weather is good, the food is pretty good (don't miss the plate lunches in Lahaina just north of town up near Safeway. Tee shirts are about 6 for $20 in Lahaina and very good quality. And if you are a bloke some of the "eye candy" is as good as you will see.
Have fun!