We like the sea days over and back and if you don't do a lot of excursioning, the cruise is actually cheaper in total than a typical 14 day Caribbean.
You also need to steer clear of all the "buying opportunities" onboard

Oh yeah - Although I got a great deal on Judy's pearls on board one time and she loves them. But we minimize the photos, the watches and the like and max the bar bill, resturant bill and specialty eating bills - chef's table, UBD, crown grill, vines...
Of course in HI, you need to steer clear of the "buying" opportunities on shore as well - except for the flea market at Aloha Stadium!
This trip we will be doing our own excursions, walking around, and we hope to get to a couple of Guy Fieri Triple D places in Honolulu!