2 points:
1) a drawback to the Amex Plt vs. CO PC that I don't think was made clear is that with Amex you have to be flying the particular airline in order to get into that lounge (NW, CO, DL). This is problematic when flying out of MSP on CO, where there is no CO lounge, and they won't let you in to the NW club, whereas they would if you had a bona fide CO PC membership. Obviously avoidable if you fly NW to begin with... Not sure if there are other examples of this.

2) I've also had experiences where the Amex FHR rate was as good or better than the best available rate anywhere else, so the amenities were basically free. At FS Chiang Mai, Thailand, Amex got us $350/night vs. $400, and we got free buffet breakfast and $80 lunch credit! At Bellagio in Vegas, rate was similar, but we got upgrade to lake view, early check-in/late check-out and $12/pp/day vouchers for breakfast. But more often than not (IME) you do end up paying extra for the amenities, so it isn't always worth the fee.