He has a few options, none of them completely effective, but offering some hope of protecting the flock from delusions.
First, prompt investigation of the type which demonstrated that the blood coming from the Padre Pio statue was from a female. That cools people's jets pretty quick.
Second, sound preaching and teaching so people realize that deception, delusion, and indigestion are far commoner than genuine mystical phenomena. That alerts people that the source of an "apparition" may be hoax, hell, or a hamburger.
Third, prompt ecclesiastical sanctions against involvement in spurious mysticism, especially by the clergy. I understand that the very dubious Vassula Ryden has spoken in churches with priests and bisops looking on. This rubbish has to stop.
Fourth, encouragement for public displays of legitimate piety, such as Corpus Christi processions, pilgrmages to shrines of Mary and the martyrs, the solemn public proclamation of fasts and the celebration of feasts. I suspect that if people don't have authentic public ways to manifest the Faith, their unattended "hunger for holiness" will give the hucksters a luster of undeserved attractiveness.
JP2 talked the talk. Looks like B16 will walk the walk (and not a moment too soon.)
I agree with waht you said but as to Vassula Ryden there seems to be a drawback from the condemation that they issued earlier.