I have no problem with websites and twitter pages for robotic spacecraft to get the public more engaged. But why not just let the people on the project express their personalities? Certainly they're excited about their spacecraft and what it's doing, otherwise they wouldn't be working on it.
I'd think most members of the public would have an easier time connecting with a flesh-and-blood human, even an engineer, than a cutesy made-up "persona" that would, I think, insult the intelligence of all but very young children. But that's just my opinion.