The prostitution is a non-story to me. Prostitution should be legal and accepted anyway.
But tbf, I think cheating on a partner (provided his wife did not agree to it) may well be the worst non-illegal thing you can do to someone. I think it is even worse than a lot of illegal acts. It is something that a lot of people might fairly judge someone's character on. Does that make it sufficiently of public interest to override the privacy? Does it affect Vaz's ability to do a job? Difficult questions tbh.
The fact this is all relevant to the committee he's on adds a bit of spice and genuine justification for the media too. Plus the drugs.