Thanks for the replies. It appears that Platinum, in the real world, doesn't offer much more than Gold.
I truly like Marriott for its consistency of product, but I will probably change strategies soon. For the remainder of this year, I will concentrate on obtaining some status with Hyatt.
After the beginning of the year, I will use my stays, where possible, to obtain top level with Hyatt. After that, I will concentrate on Marriott to retain Gold there and drop Hilton.
Thanks again for your comments.