The Privilege only extends to papers etc that are directly connected to their legislative duties. The Executive absolutely cannot be looking at legitimate working papers of a Representative. Nor can any judge authorize them to do so.
The problem was how to get to the evidence without seeing the legitimate legislative papers that were there. The officers in the "filter" team did see such papers. So Hastert does have cause to complain.
Though I don't know what else could have been done except get help from the House to conduct the search.
Elections? Fine and good, except we wouldn't know that the guy was corrupt if he was out of reach, and so we couldn't use elections to oust him for corruption because we wouldn't even know about it.
Anyway, the FBI got this guy clean, it seems. Their informant paid off the bribe, got it on video, and found the cash in his freezer. The FBI did just about everything they could to protect the rights of Congress. They even subpoena'd relevent evidence to no avail. The raid was the last resort. It hardly seems abusive, in this case.