I think it'd be really hard to go overboard with Kobato, honestly. She's just an energetic person! Also, to respond to a point you made to an anon above: it didn't come across as you trying to make the Halloween log a Kobato thing AT ALL. That's just how she is and her passing out candy and being adorable is so quintessentially her that it's just awesome to see her interacting with everyone and giving everyone a chance to talk with her!
I think that her actually healing hearts would be an awesome plot idea! You should take it up with everybody for sure. I think that, given that it's Kiseki and everyone is an emo kid it seems, she'd definitely have plenty of opportunities to heal some hearts!