I recently traveled to Dublin(the Shelbourne Hotel), London (Marriott County Fair) and Paris - I have been a Platinum or Gold Member since 2008. This year I have 62 overnights. The trip was to celebrate my 20th Anniversary. IN Neither of our three cases was a I granted a room upgrade. In fact, the host hotels seemed to 'treat you' as you were using points and not as paying customers. I used nearly 400,000 points for our stay - communicated often (with NO response) with the Gold Line and each host hotel - and recieved NO courtesy.
I strongly recommend using your points for Caribbean Travel - and enjoy yourself.
DO NOT ever stay in the Marriott Champs Elysees! You WILL regret it.