I've had the Amex Plat card for a few years now and here's why I think the card's worth it:

1) Airport Club Access + Priority Access Membership
2) Fine Hotels & Resorts **This is a great program if you do your homework
3) Entertainment access. This is the concert tickets. It's not for all shows, but works on Amex sponsored events. You still pay full price for tickets, but you get access to good seats. I bought front row Dave Matthews tickets last year. It was great.
4) Concierge can be helpful with dinner reservations and travel arrangements.
5) $200 airline fees reimbursement
6) Various other little business things
7) No foreign transaction fees
8) Membership Rewards

Here's what's not worth it:
1) Business Class Companion Tickets. You have to buy non-refundable, often full fare tickets, which are usually more than (2) discount biz tickets.
2) Cruise program
3) Some of the supplemental purchase protection/insurance. Read the small print, you don't really get much coverage

Just my 2 cents.