You're right from a 'getting a case in court' stand point, but I don't think most of the spying/tracking is about getting a case to court, and as the SilkRoad trial MIGHT have shown, the gov't just needs a way to show that they were able to track you down. They can probably make up a way that they did it after the fact if their initial search was in fact illegal.

Please don't turn this into a debate about SilkRoad, I'm using that as an example of something that might have happened, I'm not saying it did or didn't. That is for other threads.