Correct that this appears to be their argument, but that argument holds not a chance. Imagine if police searched houses randomly but "weren't allowed to use what they found unless they got a warrant." I believe this argument will be squarely and unanimously rejected by SCOTUS.
> Imagine if police searched houses randomly but "weren't allowed to use what they found unless they got a warrant."
The main remedy for illegal police searches is exclusion of the evidence if, and when, the government attempts to use it in court (and then, usually, only if they attempt to use it against the specific person whose rights were violated by the search, and not always even then [e.g., good faith exception, and other exceptions to the exclusionary rule].)
That's the main remedy in criminal court. If the police unlawfully search your house, you can also sue them in civil court for both money and injunctive relief.
It would be like if dogs sniffed your house, and their reaction was recorded, but not seen by anyone. And the recording could only be viewed after a warrant was obtained. The NSAs argument is that you can't become a suspect as a result of the recording. You have to become a suspect in some other way, and then they can go back and analyze the recordings.