I agree that Diamond benefits are rather weak (especially given the spending requirement!). That being said, there are some decent benefits:

1) Complimentary breakfast on weekends can be a useful perk, especially for those mainly travelling for leisure / mainly taking weekend trips (of course the "weekend restriction" is rather petty)
2) When dealing wih hotel management regarding client stays, Diamond status certainly has been a factor when negotiating deals.
3) At some hotels SNUs are completely useless, while at others there are some spectacular opportunities (incl. upgrades from ~Junior Suites to specialty suites that would otherwise cost several thousand dollars a night). Having to call Accor each time to enquire about SNU rates / eligible rooms/suites is a huge PITA, but there are some great opportunities if you look for them...