With Marriott hotels, the difference between Gold and Plat really isn't much when dealing with possible upgrades. But also note that upgrades at Marriott hotels is very dependent on the hotel itself. The vast majority of the base "city" or "business" Marriott hotels just don't have very many suites (i.e. a lot of hotels may only have 1 or 2 suites in the whole hotel). But over the years, I've had very good luck with nice upgrades (suites/ocean front/etc) at Marriott resort hotels which do actually have decent upgrade-able rooms to choose from.