Hi, hope someone can help me. We have a week to spend in the islands and have never been there before;offered a great deal for treasure island but it looks so small. Is there enough to do there for a week? We are both keen snorkelers and divers. Should I consider spending 4 nights at treasure, then 3 at Mana so that we can try two places? Castaway looks wonderful but is expensive compared to the treasure island deal-is the difference worth another $2000? Any information/advice would be appreciated.