We booked the lowest room and hoped for an upgrade. When we got there, I asked about an upgrade to a beach villa and told them I would absolutely pay for it if need be. They eventually got us the Beach Villa with Pool for the second two nights (complimentary). The staff was phenomenal and sought us out several times to say they were still looking to see what they could do. We had friends that booked a beach villa (no pool) out right with cash, so we were able to use their villa the first day to stay by the beach. If you're going to be disappointed if you don't get an upgrade, I would absolutely try to secure one with cash ahead of time. The beach villas are, as the name implies, right on the beach. I would've been disappointed had we not been moved (or had friends in one) and I will definitely pay for or cash upgrade to at least a beach villa next time.

For Diamonds they gave us free breakfast at the buffet or at the Portabello restaurant which had a made-to-order menu. Portabello was only available to Golds and Diamonds and was empty when we ate there once (we had friends with no status so used the buffet most times). One our one trip to the restaurant there were only four other names on the list, which may be why our service was so outstanding during the stay. The rest of the benefits were as outlined by Italian_Kayaker above. There was also a free 15 minute teaser massage that you could tack on to a regular one of you wanted, but we didn't use it.