Raildogg, you say in your post that we need to protect ourselves against rogue nations. What seems more likely, them getting the technology (Iran for instance) to launch a strike at us or them giving it to some terrorists to throw on a boat and blow up the harbor (only 5% of cargo is checked ... and we are "secure"). This whole missile defense system is a relic of the cold war, and though it seems less likely to trigger another arms race, its use is limited. Any decoys in the warhead would almost certainly lead to the failure of the interceptor missile, as it can currently only lock onto one target. Also, sending several missiles at the same time could easily overwhelm our defense shield. The costs of this system are ridiculous, over 10 billion a year and we have a 5/8 success rate in optimal conditions. So far, the two tests that were not in optimal conditions have failed.
We should focus on accounting for all the nuclear materials we are aware of, something the Bush administration only recently started to do, while claiming that nuclear proliferation is the biggest threat to America. Go figure that their rhetoric only began before the election and I haven't heard anything about it since.
Point is, missile defense is not useful in basically any situation. A nation that has technology sophisticated enough to build ICBM's has no trouble throwing decoys along with the warhead.
Our threats are more likely to come from unusual means that ICBM's, and that's where we should be focusing our money on, not a fantastic Gipper idea.