Having multiple tiers of platinum is stupid. They would be better off doing:
25 nights = silver.
50 nights = gold.
75 nights = platinum.
100 nights = diamond.
They could return rollover nights for anyone with 100 actual nights slept in hotels as opposed to those accumulating bonus nights.
I wouldn't be against eliminating rollover nights if they made up for it by giving me a benefit for staying with Marriott above 75 nights. Like Delta's lounges, the lounges at Marriott properties are often overcrowded because there are too many elites -- way too many golds and probably too many platinums. Moreover, there is not enough clarity as to requirements and the supposed benefits of platinum-premier, so why should I keep staying above 75 nights if it is unclear if I will receive platinum-premier? And it isn't as if platinum-premier gets you better benefits at properties.