The #1 reason to become a Diamond is the availability of properties for reward stays. As a Diamond I have never been told there is "no availability" for an award stay. As anyone knows try this if you are a Gold or anything less. A second diffence I have noted in staying outside the U.S. is that lounge access is almost always granted to Diamonds and not to other membership levels. If you make Diamond by the end of March you will have two years of these benefits.