Loved Maui. Snorkeling/whale watching on Molokai Sea Cruises had an open bar at a great price. Also would suggest the Haleakala sunrise & zip tour. I think we went thru Skyline Hawaii. Road to Hana is great and would be fun in a convertible. The best thing about it is you can do it at your own pace/stop where you want. I downloaded an app that was interactive and talked about the stops as you made the drive and then you could decide if you wanted to stop or not.
Years ago we did the Haleakala sunrise and bike tour. Don't worry if you aren't in shape for biking. It is a 40 mile plus tour from the summit (10,000+ ft.) to the ocean and you need to pedal for less than a mile on the whole thing. You also stop as a group for breakfast at a diner half way down. Be prepared to not see the sunrise though. Even on the morning we went it was a beautiful clear night but the clouds rolled in just as the sky started to lighten up. Still worth it.
If you go up to the summit at another time, don't just stop at the visitor's center. Make sure you continue up a quarter mile or so to the true summit. On a clear day you can see the big island. From the visitor's center you can hike down into Haleakala Crater. It is a strenuous hike at altitude so take water and a snack and take your time. Remember that the hike out will be three times as strenuous as the hike down into the crater. We met a couple from the Denver area. Strangely enough us flatlanders were fine but she struggled with the altitude. You never know...
When you take the Road to Hana I would recommend your destination be the seven pools at Ohe'o on the south east side of the island. Then take the Pipiwai trail hike. It is a great hike partially through a bamboo forest (talk about an invasive species taking over an area) culminating at the foot of the 400' Waimoku Falls. A breezy day makes the bamboo forest unforgetable because the swaying bamboo squeaks and knocks as they bump into each other.
Don't forget the Road to Hana is not a drive you should take lightly. It is a fun drive but be prepared at each turn for the unexpected around the curve. Many people take up more than their half of the road and there are frequent rock and mud slides especially if it has been raining. Have fun, but proceed with caution. Take your dramamine if you get motion sickness.
You may check out a lava tube and black sand beach on the drive to Hana or back. We stopped at one small black sand beach and had it completely to ourselves. Always be aware when posing for pictures in the surf. Big rogue waves can break unexpectedly at some of these beaches and create a picture you weren't planning.
When in Lahaina make sure you check out the Whalers Village Museum. It isn't anything big, but it helps you understand what Hawai'i was like post European arrival but before it was all about tourism. The aquarium at the Maui Ocean Center is worth a stop. It is right near the junction of the road that goes west toward Lahaina and Kanapali.
For a shorter drive on a day that may be too wet for beach time but not a total wash out try Iao Valley.
If you go to one of the beaches in Makena State Park south of Kehei and Wailea, make sure you take the road further south. The road ends in the Ke'one'oio lava fields.