Marriott Rewards has routinely alleged (and you can read the blogs both here and on Insider as well as 3rd party blogs) that the catagory changes are based upon redemptions so popular props with high redemptions can be expected to increase, and vice-versa.

While I "might" buy into this theory, it still does NOT account for how they establish the catagory of new properties because they would have no redemption history! For instance, the soon to be opened Hua Hin Marriott is now listed as a Cat 4 (the demolished one was a Cat 5) - great deal especially for New Years Eve when the buy rate is well over $300/night++

Great advice - just like airline miles - earn and burn.................