We stayed at the Singer Island location last August. I can't comment on their treatment of Diamonds as I was gold but I found the staff to be lovely and would go back to this hotel in a heartbeat. The Singer Island beach was beautiful, chairs, umbrellas and towels were available for use by the guests (cabanas at the pool, none on the beach). Poolside and beachside service as well for drinks and sandwiches/snacks. The beach is basically steps from the hotel, you walk outside and you're on the sand. Keep an eye out for interesting shells and for staked off sea turtle nests. It looks like only the ocean view rooms have actual balconies that you can sit out on.
There are also restaurants a reasonable walk from the hotel if you don't feel like heading into WPB proper.