A couple other random thoughts:

- Hawaii has fanastic hiking, but many of the attractions are easily accessible by car. Even a short hike away from the parking lot can get you away from the crowds.

- Convertibles are sweet, but you should also think small. If you can parallel park somewhere that bigger cars won't fit, you'll get a better space near some choice beach.

- On the flip side, you'll see lots of Jeeps that you can rent. Some travels really require four-wheel drive. In particular, if you're planning to drive across the big island or to the top of Mona Kea to see the telescopes, then a Ford Focus isn't going to get the job done safely.

- I don't think there's a bad time of year to visit Hawaii. However, every island seems to have a sunny side and a rainy side. Make sure you pay attention to these issues when booking your stay.

- Get a good guide book. They'll clue you into restaurants, oddball stores, and everything else. My favorite clue concerned Volcanoes National Park. They have a deliberately under-publicized lava tube tour. It's low impact, beautiful, and only costs you a pack of AA batteries, but you have to sign up in advance. It's worth planning a trip around the schedule for that tour (which I think only happens once or twice a week).