I think good (i.e., legitimate) questions should remain open forever. Whether a question has an answer or is followed up by the question OP, is irrelevant to whether the question might be useful on the site - for others, for example.
What really matters is whether the question is clear and appropriate for the site.
I don't know what it means for a question to be "uninteresting". Even if that were specified, I'd probably doubt that any automatic culling based on whatever that might mean is a good idea. Question quality is specified well enough, I think. Question "interestingness" isn't.
@Tyler's point about questions that are "too local" is a criterion about question quality. Question quality is independent of how long a question might have remained unanswered.
A question that was appropriate when posed could conceivably become no longer appropriate for the site - e.g., it might become outdated in some sense. But that's rare, and in any case it should be handled by simply closing or deleting it (manually), i.e., case by case.
My question here is about why we have a much lower percentage of closings.