I was a diamond from 2008 through early 2012....I switched to marriott last yr...got tired of Hilton's and staying there 190nights a yr...just wanted a change.
Regarding suites, it's def dependent on the hotel. Notably, At the Bentley south beach, doubletree Santa Barbara, and hilton Glendale I received huge suite upgrades.
Even with marriott, I just plain ask "do you have any suite upgrades available". You'd be surprised how often it works.