Watch the Nastophonics online guitar lesson by Jennifer Batten from Rock Sauce For Lead Guitar
Like any specialty technique, it can get old if you overdo it. Pinch harmonics should just be used for a limited number of notes in your phrase for emphasis. It's akin to typing a whole paragraph in all caps instead of just capitalizing the few words you want to emphasize. Too much typing with all caps loses impact. If you do a certain thing too much it takes away from the specialness of the effect. But then again as soon as I make such a "should" statement, I think of Billy Gibbons' "La Grange" solo where the one take away from the solo is how many pinch harmonics he did in a row! I believe he also used a Mexican peso coin to help get those harmonics. Metal on metal will give you a different sound than the usual pick materials. The pinch harmonics are part of what makes that solo so memorable and iconic. But he certainly doesn't do that in every solo.