Well, the NSA has been operating illegally anyway, pre-Snowden they had hidden programs (which were leaked in the New York Times, then when the EFF tried to use those NYT articles in court, the feds claimed the New York Times aritcles were classified and inadmissable.) There've been articles about how, the few times FISA actually said "Hey you have to cut this and that out", the agencies made non-sensical circular logic arguments to justify their illegal activities being legal even if FISA says they are illegal. So I doubt that's stopped.
BUT, not passing this law begins to swing things away from people like Obama who want to "balance" rights or privacy (which means taking rights or privacy away) towards people who recognize the Constitution guarantees these rights and want to have these rights. This move alone won't do a thing but will start moving things towards the attitude that will reign in the NSA.