here is just my two cents:
we did not go to any Luau OR the famous Warren and Annabelle's Magic... I am sure they are good, just not for us... My dad enjoyed his Luau in Oahu, though
places I think worth visiting in Maui:
1. Haleakala summit, sunrise or sunset. do you have kids with you? if not, go hiking down the craters, it is like you are in Mars and you will see the silversword you won't find ANYWHERE else (12 miles at 10,000 feet is not good for kids) (half day trip)
2. snorkeling, Molokini seems a popular place and I recommend pacific whale foundation (a half day trip)
3. West and North Maui: the blowhole, Olivine pools and so much more... if you have a GPS, take it, some sightings are so difficult to find...
4. Makena/Wailea beaches...
5. Optional: Road to hana and Iao valley...