The major difference, IMO, is the ability to change/redeposit awards with no fee. There's also lounge access for Platinums on int'l itineraries (though with the *A move, it's believed that benefit will extend to Golds as well).

Other than that, the levels are much the same. There are a couple threads out there on Gold vs. Plat, and the general concensus is that it's about the same, and it's not worth going out of your way for Plat. That said, if you're going to fly it anyway, there is some incremental benefit.