Cannot speak to the Platinum issue as I am only a lowly Gold. I have stayed in both the Aloft and the Westin at the Domain in the last year. Skip the Aloft -- it is very noisy for some reason and the beds are not comfortable. The Westin was very nice, and they were nice to my non-status co-worker who was with me, too. He was suitably impressed and told me so. Maybe it was the fact that we got stranded due to the Dallas ice storm and they were sympathetic. Or maybe they are always that nice. His room was on my reservation, but still, I am only a gold, not a plat.
I have not stayed at the other Austin properties in quite some time, sorry.