If international flying is a significant portion of what you do, it's really silly to fly NWA. They have said that WBC upgrades are not a high priority to them, and they've slimmed down total WBC inventory over time. They've even removed moved 'Rulebuster' WBC awards from J inventory to C inventory so they can be assured that no matter how many miles you have, you cannot get a WBC seat unless they free it up.

Basically, NW is a program that makes sense really for domestic travellers.

Steve