Carrots Are For Rabbits
Gregory Scoblete explains in this TCS article why economic carrots or sticks won't have any effect on Iran or North Korea's pursuit of nuclear weapons. Military sticks still a possible deterent however. In Iran's case, if they were convinced we would attack them if they did not abandon their nuclear intentions, they would in fact probably abandon those programs. Of course, since we are probably not in fact willing to attack them if they don't disarm, convincing them of this will be difficult. Military action against North Korea is probably even less likely, although China's power over North Korea remains strong enough that it could force NK to abandon it's weapons. Our diplomatic efforts have been focused on getting China to do this, but so far we don't seem to have enough leverage to make this happen. My bet is that the one thing that would make China get motivated, and take decisive action, is a credible threat to arm Japan and South Korea with nukes as a result of North Korean nukes. This approach though has two difficulties. First, both Japan and South Korea would be tough to convince to go along with this. Secondly, the very concept of nuclear non-proliferation goes against using this approach.