Molokini does get crowded. Head up to the snorkel boat that leaves from the Maui Prince hotel beach. It is the first boat out there.
You picked the best luau....
If you want a real cool/good restaurant to check out, go to Mama's Fish House in Pai'a. Quaint, on the beach, great food.
http://www.mamasfishhouse.com/
A drive up Haleakalā is pretty spectacular. Last time I did it, it was 46 degrees up there...bring a light jacket.
The road that wraps around the north shore is something not to be missed. The beauty is epic.