You can still look for cancellations.
To be honest, I am not sure I would want to be on a ship that is filled with 80% Platinum CC members. You will not be able to book anything popular on board (excursions, special dining, tastings). Also my experience is that that demographic can sometimes be a bit entitled. Not saying everyone is like that, but on my Panama Canal cruise that had more Platinums than any other cruise I had been on, there were people who behaved like they owned the ship.