I am both a NW WC member as well as a PP cardholder (thanks to my Citi Chairman card). I found that PP is great, but not very useful to a NW WC member who flies Sky Team airlines. That's because I can already access most of the lounges in the Sky Team-served terminals, especially in the US.

I suppose if I traveled to more foreign destinations (especially smaller international airports), PP might have been more useful.