This may be a reply too late for you but just to let others know about parking for the ferry. Last week I took a 1/2 day tour to Lanai arranged by the company who runs the ferry to Lanai. When asked where I could park the ferry company suggested that I use the pay parking behind the Wharf Cinema. By showing my ferry ticket stub I got a 50% discount on the parking which was $5 for the day (I parked around 8:30 and picked up the car at 3:30pm. When I paid the attendant he told me that the discount only applied to people who take the ferry the same day and not those who stayed overnight.
Note that when I parked it was early so the attendant was not there. When I returned from Lanai I found a ticket on my windshield which I had to give the attendant. It is an open air lot but luckily I found a shady spot. Lastly it is about a 10 min walk to the harbor. As the ferry was pulling out a couple came running down the dock and begged to be let on. They said that they didn't realize how hard it would be to find a parking spot and that was the reason for their lateness. Luckily for them the ferry stopped and let them on.
I was staying at a hotel in Kanapaali so I could have taken a taxi from the hotel or the public bus and would have avoided the parking issue. I think this would only work for those who are taking a day trip. As I was waiting on line for the ferry I saw a number of people arrive by taxis with suitcases and golf clubs guessing for a stay at one of the Four Seasons on Lanai. They could be coming from as far as the airport....