All of those but possibly Boston are essentially mentally ill people who went nuts - domestic attacks. The NSA is usually tasked with dealing with foreign threats. So your complaint is, by and large, mistaken. Your complaint is better directed at local police and mental health facilities.

It's almost certain that the TLAs generally tries to keep within the law as they see it, and push the boundaries as far as they can - this is the trend of the executive branch. I would expect them to have batteries of lawyers hired to find out exactly what is permissible, and then to do all of it.

It'a also entirely disingenuous to say that the TLAs have no purpose. To riff off of @leashless from Twitter - they are a reaction - an immune response - to some entities which do and did some very bad things covertly, and are now being an autoimmune disease on the host state. The truth is, 9/11 gave a rather large blank check to the industrial/ security/intelligence companies and agencies in the US, and most people were not in the mood to worry about civil liberties too much at the time. "Never again" was the refrain, and that sort of perspective removes all ability to do a cost-benefit analysis. So they expanded with that attitude and that check... then, like beauracracies do, they entrenched and began to expand power and capabilities. This is not new behavior in any bureaucracy. This sort of eventuality was, as I recall, predicted quite loudly after the Patriot Act was passed.

Don't understand why you list unthwarted attacks. The real question is how many attacks were thwarted. That is the point of disagreement.