My opinion is that we shouldn't shut the NSA down - they DO serve a valuable purpose for National Security.
What we SHOULD DO is force them to obey their charter and the law. If they want to spy on foreign nationals, crack enctyption, etc.. go right ahead.
If they DO sweep up some US citizens not involved in plotting against the US.. ok, that may happen tooo - but they should NOT be allowed to share results of illegal wiretaps/surveilance with law enforcement - and any evidence obtained in such an illegal manner should be inadmissable in court.
Basically, let the spooks spy all they want for actual National Security purposes, but don't allow that to become yet another extension to the already too long arm of the law.
I know... it's such a juicy target:
"We were watching this guy because we thought he might be a terrorist but instead we uncovered that he's a drug smuggler... here you go FBI / Local Law Enforcement, you can use this to get him off the street."
well... as much as it might suck to let some guilty people get away with it because the evidence wasn't obtained legally... it sucks more to treat your citizens as the proles and outer party folks in Orwell's 1984 - the damage to society from pervasive surveillance and selective prosecution using the results of said surveillance is (to me) far greater.
Let the police do their own footwork - hell, if you can get a court order to "wiretap" someone fine... but we are a nation of laws and when the government forgets that, we all suffer.