I also have a feeling Nel is more than she looks like. The other two arrancars seem to be pure useless comedic sidekicks (at which they fail completely as far as I'm concerned, except for the useless part where they excel). Nel, however, just sticks to Ichigo and in my opinion she hasn't really been yet proven one way or another, as if they are saving her for something. Maybe she has a release or something (though I don't remember seeing her with a sword), and she will save Ichigo in an important furute fight.

Though it might be just my logical mind speaking. After all, I wouldn't understand why they even exist if none of them have some fundamental role. So far they have been all without any purpose. And honestly after the past eps I'd like to see Nel with a good role rather than either of those two bloody idiots.