The most common upgrade is a regular room on the concierge level, which may even be a floor or two below the floor where the lounge is.

When you say you "just" made Plat, when was that, and is it showing on your account online yet? If you just had night 75 in the past week, it may not have hit your account yet.

Of course, lounge access is given to Golds too, so you should have gotten that anyway.