I've found Dispel to be useful in X, although only very occasionally. For instance, when an enemy uses reflect on itself then, like the Seymour on Mt. Gagazet I think it is, attacks themselves to reflect it onto you (a pretty stupid strategy if you ask me). Also, when say, a dark element uses reflect on itself I like to use Dispel. Mostly because instead of beating them down physically I like to use Lulu as well to give everybody a chance in battle.

But for the most part Dispel's pretty useless.