You're forgetting Priority Pass.

I used to have a CO PC membership. I once tried to use the PC card to get into the holodeck in heathrow. This is a KLM affiliated lounge and I was flying klm that day. This was JUST before everyone joined skyteam. They would not let me in.

They would also not let me in the KLM lounge in AMS when I whipped out my PC card when I was on an easyjet flight.

Priority Pass is really the king card for lounges. It's also $400 and it gets you (not with a second person) into lounges pretty much everywhere, including almost everywhere the CO does, and a couple hundred airports more. You wouldn't realize it until you're sitting in a lounge in Curacao...

I have the amex plat AND the Priority Pass. I JUST got the amex - so I have not tried to see what it cannot get me - but I really think that I get my money's worth out of these lounges.

Except Delta - their lounges suck.