We were on Maui in September for our honeymoon.....We are saving up our miles to go back, it was amazing.
DO: road to hana (remember to bring bug spray in addition to the sunscreen), get a picnic lunch and the narrative cd before you go and ,make sure to see the painted eucalyptus trees in the kenae arboretum, on your way back eat dinner at mama's fish house; haleakala - a nice option is do drive yourself up for the sunset instead of the sunrise; great restaurant at the Grand Wailea, also Seasons at the four seasons is great; we didn't get to go snorkeling but I would reccommend it; also the best luau is the Old Lahaina Luau - you might want to spend part of the afternoon in the town.

Hope you have a great trip!

Amy