Hi Heidigale,
We just returned from the 12 day PG cruise so some of our itinerary was different than yours. However, here are my suggestions for things we did on the stops that are the same:
Bora Bora: if you like to snorkel I definitely recommend the Sting Ray/Coral Garden trip. We were completely encircled by rays and white tipped reef sharks on the first part of the trip. The boat then moved to the Coral Gardens for beautiful snorkeling. Everyone loved it.
Moorea: we rented a car and drove around the island ourselves. You could also rent the little buggy-type cars which also looked like fun. If you pre-arrange a car for 6 that would be a better way to go than taking a cruise tour. You could stop along the way and snorkel or just see the beautiful island. We spoke to some that did a snorkeling excursion and thought it was so-so. My other suggestion is to take the Dolphin Watch trip with Dr. Michael Poole. You'll get to see some amazing dolphins and he stops for some snorkel time as well. We did that before the cruise because we stayed on Moorea for 4 days beforehand.
private Motu on Tahaa: We had a pretty rainy bleek day on the Motu. Some friends of ours took the morning drift snorkel trip and loved it. They saw a lot of fish while they were wisked along with the current.
Tahiti: We had an extra day at the end and we rented a car and toured all around the island and enjoyed that.
As you can see, we're not big on group excursions and tend to do things on our own. We never feel satisfied with sighteeing trips on cruises. They are just not that great. However, if you like to snorkel that is the easiest way to accomplish it through the ship since you might be able to arrange things yourself on shore but you have limited time.
Regarding dinner reservations, I was a bit anxious about that since I didn't make any prior reservations from home. My husband didn't want to be so constrained ahead of time. Bottom line was we never had trouble eating in the various restaurants, especially if we were willing to wait a day or so. We also really like L'Etoile the best! La Veranda was nice but had a more limited menu that only changed once a week. The food was good at Le Grille but it's humid and dark this time of year and not that comfortable.
Hope this helps.
Linda