-As an Oceania newbie, I too was confused about the OLife amenities. From what I learned on this forum, it is generally more advantageous to you to go with the shore excursions amenity. You can choose the tours that aren't marked as "OS" Select. In our case, we chose 3 tours that came to $579 per person x 2 = $1158. That's a heck of a lot better than the $600 total OBC. There were a good amount of tours to choose from for us, but that will depend on your itinerary. So if you're going to a destination where you know you'll be happy with cruise line tours, this is the best option.
-You will get a credit for the airfare, which is what we did too since their bus. class air was $2,400 more per person that what I could get on my own.