I'm mostly with Jane Hamsher on this; given the importance of that seat, and the importance of having an effective legislative fighter in that position, it doesn't make a lot sense to give it to an untested rookie who's never passed a bill in her life.
However, I think we all understand what's going on here, and it's not simply the oligarchical politics of dynasties. Kennedy brings real star power to the position. Caroline is not like the other Kennedy offspring; she's managed to maintain a certain mystique that, like it or not, will be a tremendous fundraising draw on the stump. Of course, we have no idea if she'd be any good at all with a crowd, though her appearance at the DNC this summer was impressive.
The problem is the flip side of the reclusiveness that has kept her persona as the Princess of Camelot intact -- namely, we really have no idea who she is: what her positions are, her values, her vision for Democratic leadership and effective legislative craftsmanship.
She may in fact possess all these, and previously unglimpsed leadership qualities as well. Or she may not. We just don't know.
So if Kennedy is serious about the job, the first thing she needs to do is open herself and let the public see who she is and what she is about. Until then, it doesn't make sense to even think about handing her this job.