The call-us-when-he-wakes-up thing could have just as easily been done by the hospital staff as it was by Meg (and frankly, they'd have been more reliable about it). Meg didn't destroy the demons at the hospital, Cas did, and while she did bring up that he could, Dean already knew it and likely would have decided to use him even without her once he decided there was no other way. She's not crucial in either instance, but was written anyway in just so she'd have something to do.
Crowley isn't a threat right now, sure, he might become one later, but you could say the same thing about Meg. Fact of the matter is Crowley is only has minor importance to the plot right now, and Meg and her fight with him have even less.
I suppose it could also be a setup for next season - so that if and when Meg & Crowley pop back into the season, they have a bit of background as to what they have been upto for the past year