Bob, Oh I wish I was going... it has been far too long.
Am I missing something in your arsenal of glass... No weather sealed lenses?
My memories of Maui have lots of warm "out of nowhere downpours / drizzles" and lots of sand. It would be great to have a DA50-135 for those days, which were almost every afternoon if memory serves
Maybe it's time to sell one of the superzooms and grab a sealed lens.
If not, I would toss in the 21 (does not count because it is so small) the 31 / 16-45and one of the superzooms with the 55-300 being a my choice. Unless you are really happy with your copy of the 18-250 and then the 55-300 stays home.
Have a great time... and post some beautiful shots when you get back....