Mantas on Bora Bora, IMHO, trump the sharks there. (But we were jaded by the Rangiroa Shark dives, which was the purpose of our trip, and likely beyond the scope of yours.)
We loved bicycling on Bora Bora, and renting a Scooter to traverse Huahine. (This was 10 years ago, on our 20th anniversary blowout.)
The main market in Papeete, Tahiti, is a great place to browse and shop for anything from food to expensive jewelry.
Beautiful islands. No surprise that it is a pricey destination, but we thought well worth it.
Are you on the Paul Gauguin? Impressive vessel, to say the least!