Taking the advice from this board, I called on the day of arrival to check upgrade availability. After being shuffled between front desk, reservations, and "at your service" desk, I was able to go from a concierge level upgrade to a confirmed suite!

Upon check in, the fron desk supervisor looked at my reservation and declared "we have a fabulous upgrade for you!" It was a large corner suite with a balcony and full view of the waterfront....unbelievable. Yes it was low season and midweek, but what a wonderful way to spend time in Seattle... so I extended my stay one more day to enjoy the impressive suite. This experience definitely makes being a Plat worthwhile!