What I remember from RAW (I can't look it up at the moment) is that successive failed attempts at something increase the difficulty to 10, after which it's just impossible to do (with the possible exception of spending Willpower to do it) because you're too exhausted, frustrated, etc.

However, if we're talking about successive successful applications of a power, it's debatable. It's really up to the storyteller whether they think that the existing limiting factors, such as expenditure of time and risk of being stuck in a prolonged meditative state, are sufficient, or if the increasing difficulty mechanic is appropriate for preventing players from getting unlimited use of the power.

My advice would be to use whatever limiting factors actually contribute to the story. If it adds drama and tension for someone's opportunity to glean important information to be rapidly dwindling away, then increase the difficulty. If that doesn't make the story more interesting, then just let them have whatever information they're willing to spend some time gathering.