Having been Platinum for the past few years and Gold before that I can say that the international upgrades are few and far between and then only when Coach is overbooked. NW is really stingy when it comes to these upgrades and using miles for upgrades internationally is difficult except on the highest fares.
In terms of benefit packs, that is a big disappointment as well. The perks for Platinum are really just the domestic upgrades and the 125% bonus miles - not very different than Gold. On the website there are a couple of hotel and car discount benefits, but nothing extraordinary.
Hopefully NW will get more competitive in this way at some future point. They're even behind their partner, Continental.