I'd argue that most successful politicians already are highly effective instrumental rationalists when it comes to getting elected and staying in office.
If by "highly effective instrumental rationalists" you mean "good at winning", that's a very defensible position. That said, I'm not sure it makes sense to use the terminology that way unless you want to commit to Usain Bolt being a highly effective instrumental rationalist when it comes to the 100 metres.
(If you're reading this, Mr. Bolt, well done on your many successes.)
Has no one else mentioned this on LW yet?
Elizabeth Edwards has been elected as a New Hampshire State Rep, self-identifies as a Rationalist and explicitly mentions Less Wrong in her first post-election blog post.
Sorry if this is a repost