We won't really know whether it's worth it or not until ToB comes out.
However, if I understand correctly, it is supposed to be a remnant of what happened to magic during the Time of Troubles (i.e. magic became unstable due to Mystra's absence). Therefore, wild magic can be *much* more powerful than "normal" magic, but it is also much harder to control. I believe that every time you cast a wild magic spell, there is a chance that it goes awry and causes an effect that you didn't expect or blows up in your face. However, if it comes off properly...it could be a very powerful weapon. Imagine a triple-decker fireball, for instance.
