Rhodes is Very Nice. The 2nd largest Greek Isle after Crete. It has a rich history from the Crusade time. Very impressive walled city right by the harbor. When we did our first Greek Isle hopping, we took an overnight ferry leaving Santorini around midnight, reached Rhodes next morning. We booked a small cabin - the steward met us at the Santorini dock when the ship arrived, then we waited at the lower deck for the crew to reverse the escalator direction. After that the steward took us to the passenger deck check in counter. After check in he walked us to our cabin. The next morning when we were trying to disembark with the crowds, someone came to fetch us and took us to an escalator so we did not have to walk the long steps. We booked our cabin when we were at Santorini, at the Blue Star office in the :"downtown" of Fira.

You will fair far better by booking independent lodgings than the Mystique or any other SPG properties (very overrated). In Sept you should be able to find cash booking at the Indie that cost similar or less in point "value" conversion and most likely have a better time.

Personally I dont feel using a boatload of points on the Greek Isles is good value other than people keep looking at the retail rates and feel they have saved. In reality the same amount of pts would return far better value at locale that is not outrageously priced by the chain hotels. Again, you can find some very nice indies even the real "cave" settings, at better prices with more spaces.

Hint - look at Imerovigli area and avoid the now super commercial / touristy Oia that is where the Mystique is located. You actually get a much better frontal view of the half crater from Imerovigli.