That would be a 'no brainer' choice for me....take the train and the cruise...you'll love them both!I am comparing a first class plane flight to Hawaii to a roundtrip train trip to LA (to catch a 15 day cruise witih only 4 days in Hawaii) with bedrooms on Superliners and Roomettes on Viewliners. The fare for flying first class was less than the train trip, on the days I compared. I have not flown in about 15 years (due to ear pressure issues) but may consider flying to Hawaii some time in the next 5 years (or take Hawaii off my bucket list).
If you don't want to be on the ocean that long, there is one ship, ( NCL's Pride of America) that does a seven day island hopping cruise solely around Hawaii. You could fly from home or from the west coast to get there....