Thanks for the recommendations. We generally enjoy our Bloody Mary's with breakfast and the boat tour serves cocktails (included), so driving is out of the question. The rep at Kauai Taxi has been great to work with so it should be very enjoyable.
Lesson learned: the tour website indicates 1:15 check-in and four to five hour duration. I called them (fortunately) and was told that while they begin check-in at 1:15, the boat actually sails at 2:00 - 2:30. They time the return for sunset, which is 7:01 PM. So, while I originally scheduled the return pick up for 6:30, I had to push it back to 7:30.