<p>One clear principle has consistently helped me moderate such situations: </p>

<blockquote>
  <p>If your intended changes affect only your work, feel free to make them.  Indeed, we encourage you to do so.  But if they might affect the contributions of others, then be careful!</p>
</blockquote>

<p>By "contributions of others" I mean principally answers that may have been posted in the thread, but I also include comments of substance.  Thus, for instance, if anybody has answered (and <em>especially</em> if such an answer has been upvoted), then unilateral deletion of the thread is considered to be "self-destruction," which is not a good thing.  The system actually flags such acts for moderator review.  If there is a comment thread that illuminates the nature of the question, such as providing links to related materials, pointing out misconceptions, or whatever, then you should also be reluctant to take any action that would remove that material from public view.</p>

<p><strong>In the present case, where a question has garnered no comments or answers, the best approach is to edit it.</strong>  An edit puts the thread into the community's review queue, which will bring it to the attention of the many people who routinely review that queue.</p>
