To me the only real benefit that I feel I get from being Hilton Diamond is the ability to book award stays at properties when all allocated award bookings are already made and the 50% bonus.
I went to Savannah, GA with my girlfriend in April and the hotel (Hilton DeSoto) was not completely booked but had rooms left at the rack rate of $245 two weeks out. All award stays were gone since a long time ago. No problem. The diamond desk got me a room anyway and I was upgraded to the top floor. Very nice stay and I would not have been able to stay in downtown unless I had been diamond (it would have cost me $800 for the weekend which was out of the question)
Sven