It's okay and recommended to do the occasional cleanup every now (we have to keep our quality at a certain standard after all) and then ensure that we have as little unanswered questions as possible and those that are asked have at least one useful answer. That being said there are some questions buried deep in the Unanswered tab that can't be answered due to insufficient or incorrect information, poor quality or some other technical issue on the user's end.
Three things I look for when deciding whether a post is worth keeping open or keeping on the site are:
- Is it localized or do you find it not helpful to future viewers?
- Does it have more than a few dozen views?
- Has the user made any effort to communicate with anyone via comments etc
- Is the user registered or have they been active on the site in the past 6 - 9 months?
If you come up with a yes, no, no, no or it matches at least 3 of those do cast a delete or close vote or flag it. Closing as unclear won't necessarily apply to all of these however and might discourage a potential answer. Also, if it has a good number of views, that means it might be a recurring problem and worth taking another look at so use your best judgement.