Kaui is certainly a beautiful island. Even on an all day tour you will only get to see a part of it. I wouldn't base a cruise decision solely on this port stop or not , but, would balance that out with the other ports, the ship and cruise line , etc.
Helicopter tour of the cliffs and Canyon (Jurasic Park stuff), Boat ride on the nort west shore , Bus to the Canyon and other sights like blow hole, Wailu River and Emerald Grotto. A day on a beach such as Poi Pu (often rated best beach in Hawaii or even in US.). A snorkelling trip, catamaran ride. Almost anything you want to do.
Don't miss Kauai, it is beautiful. Although I live on Oahu, my absolut favorite island is the Big Island, followed by Kauai, Maui then Oahu. The big isle is my fave because it is so diverse. On minute you are in desert/lava surroundings, next thing you know, you are in a tropical forest with beautiful waterfalls. Then of course there are the volcanos that can't be missed.
Kauai is beautiful also, very laid back. Nice place to really get away from it all.
Hope this helps.
I just returned from the Pride of Aloha cruise where we stopped for two days in Kauai. It was my favorite island. I would recommend that you NOT miss this island. For real fun, try the ziplining at Kauai Backcountry Adventures. It was by far the most fun we had the whole time in Hawaii.
We did the Fern Grotto and cruise down the Wailea River and it was a complete waste of time & money. It poured rain and was really boring. But we took someone's advice and we could have done much better with something else. The island itself is beautiful.
You don't want to do Napali coast boat trips in the winter. Remember in virtually all of Hawaii that the north coast of all islands gets very BIG surf and waves in the winter. Swimming and boating out of north shore areas can be dangerous, and many tour companies do not offer them in the winter for north shore areas. This means that winter is a good time to drive to north shore areas (esp. Oahu or Maui) to watch surfers, but not to get into the water yourself. In the winter in Kauai I would go to Waimea Canyon, take a helicopter trip over the Napali coast, and swim at Poipu Beach. Save the north coast and Napali coast boat trips for the summer.