I was in the same boat as you as I always try to book SPG hotels. I will be in Sin in may , and for the first time in a while I have opted away from SPG as 1) I have read bad reports about Plat treatment and 2) there is no club lounge.
I went for the MO instead. I note that you are a Centurion cardholder. You should not be paying FHR rate but Centurion rate, with upgrade at time of booking.
I booked a Harbour View Club suite for £75 a night ( staying 2 night with second night free).
IF there had been a good SPG promo I was going to CXL that and head for the Sheraton Sin instead, but with the current Promo I will stick with the MO instead ( hard to beat at that rate).
If you need any more info , drop me a line.