my wife got carsick on the drive out, but we think it was a combination of just coming down from Haleakala with elevation etc.
We spent a night in Hana, went to the local beach. The next day we did the Seven Sacred Pools (AKA Pools of Oheo aka Oheo Pools aka Oheo Gulch) which I thought was amazing but that was when you could swim in all the pools. We had a number of pools and waterfalls completely to ourselves.

We drove home the southern dirt way, no problems then, but the rental car companies like to scare you not to. The tour buses go that way. nice black sand beaches, not windy and my wife didn't get carsick.