There are loads of old stories where Batman's trying to stop a villain from stealing something. They villain may well be absolutely willing to kill, but murder isn't their goal - money/theft is. Do you think that can still make a good story, or are the stakes too low?

What about solving a single murder? He used to do a bit of that. Serial killer?

Or does it need to be threats to the entire city or even world to be big enough to really engage you? I mean, the case-aspect of the story, not the personal stuff.