Lounge access:

USAir: Anytime
Delta, American: If traveling on them that day
Others: There are a lot of "independent" lounges that accept Priority Pass Plus (or is it Select, I forget which). For example, my wife uses the Platinum Plaza Lounge at YYZ, for which entry is free with her Priority Pass card, which she gets for free with her Amex Plat.

As for the $200 fee credit, note that you can use this on only one airline per year, but it is calendar year, so if you get your card in (say) April, you get $200 to use in April through December, then another $200 in the next calendar year. There is a list of what you can use it for on the Amex site, but mostly it covers all sorts of fees such as change fees, award ticket fees, seat fees, etc. Also covers in-flight food and drinks. Does not cover in-flight internet (although I think the corporate plat card now covers 10 Gogo sessions per year). Sometimes it covers gift cards, and some people have used their credit to buy gift cards and resell them, but this is a loophole that may have closed.

In my case, last year I used it on Delta for two economy comfort fees @$19 each, and an award ticket change fee @$150 (so I have $10 left). Last year I used it for award ticket fees.