Loyalty rewards is a difficult topic. Do you do what, as others have said as per airlines etc., have a cut off period so only your activity for the last, say, 5 years count or do you reward long term loyalty. Is it based on night aboard ship or spend. Personally that is my gripe. As a single traveller I have to spend 'the single supplement ' more per night to get the same benefit as a individual travelling as a couple. My problem I know.
Whatever the solution the loyalty benefits are no spectacular for the amount one has to pay to reach those exalted tiers.