Yeah, it was known all along that counter-measures would be much easier than further development of the defense system. Besides this relatively elaborate trick, you could simply include a cloud of cheap decoys in your missile payload. That didn't faze Reagan, and apparently doesn't give W any pause either. I guess they expect to remain ahead of those 'axis of evil' states even with the huge cost differential against them.
Well it depends on whether you'll even find a single low-tech missile incoming, or something like that. Then, an interceptor could be good to have.
And of course, if you happen to have friends/patrons in the military industry who you'd like to give many many millions of dollars in government contracts.