Yet it would be trivial to defend against trivial attacks like this. They just need to set a length limit on ingested messages, clean up those regexes, and they're done. A clever NSA developer (of which I'm sure they have several) might implement a garden-variety spam filter.
We're trying to inject noise, but this noise is obvious. It's like a nation-state playing Cold War-era radio games by broadcasting "DOUBLE AGENT X COME HOME, DOUBLE AGENT Y COME HOME", etc. Sure it's noise, and it might distract them for five minutes, but it doesn't win the war.
Want to fight XKeyscore? Make the noise impossible to distinguish. Set up free email accounts that bounce randomly-generated "interesting" messages among themselves, in between notes to Mom about the World Cup. Get open source software that uses network communication to piggyback some keyword-laden (though non-incriminating) text onto messages it would send anyway. Run a Tor exit node that blocks illegal activity in your country (so you don't go to jail).
Or someone else should, at least. I'm busy. And now, I'm on a list.