I think a ship is a great way to see the Society Islands. You want to see Tahiti just because it is Tahiti, and the same with Bora Bora. Moorea is a truly beautiful island, and so it is worth taking a cruise just to see those three.
To me the beauty of the islands is in seeing them which doesn't require a week. I feel the same way about Hawaii - I wouldn't personally want to stay a whole week in one place.
It depends on your temperament, however.
It is a long way to travel, so it makes sense to spend extra time, and there is nothing wrong with seeing Hawaii on the same trip since it is "on the way."