The AMEX platinum isn't all it's cracked up to be. (I base my opinion form experiences three years ago.) When I tried to use my PLAT card for entrance into a DL club, I was told that I could only enter within 2 hours of flight, during peak club times. (This, during a 5-hour delay in ATL.)
Then, once in New YOrk (I believe JFK) I was denied entrance to a UA club, even though I had a QF - UA codeshare flight on UA metal. Was told that it needed to be a UA flt number in order to gain access to the club.
I went back to the green card, joined CO's club, and have found my club card is honored everytime I've needed it.