I also like the Amex Platinum. I had a Mercedes one because it was cheaper, and it came with a 50,000 point bonus. The price for the Platinum card is higher now and the bonus is 60,000. The business one is cheaper but the threshold for the bonus is a lot higher.
I flew between JFK and SEA, and I used Priority Pass to go to Wingtips at JFK and Alaska Airlines Boardroom at SEA, and used the access provided by the Plat card to enter DL lounges at JFK and SEA. I think the bonus will reduce your effective cost for the card to 0, or yield a net gain, not even counting the card benefits.
Scroll down the Miles and Points main page and look at the credit card programs forum - Fatwallet also has lots of good information.
There's lots you can do with credit cards, lots of points, miles, and cash you can get, and Fatwallet and Flyertalk helped me understand the best ways to work all of it.
For your present question, I reiterate along with others that the Amex Platinum is going to be very good for you, but maybe there are ways to get it cheaper, or to get more points, that that those of us here don't know.