I just edited a lot of MathJax in this question, then voted to close it. Was that a stupid thing to do?
Is there any point in editing MathJax in a question that will inevitably be closed?
Many duplicate questions are not deleted after being closed, the rationale being, essentially, that subtle changes in wording may prevent duplicates by improving search functionality. In other words, though the content is an exact duplicate, the way it was posed is not, so the question is still useful because it provides a link to the answers for future users who might also pose it that way. In this case, modifying the MathJax could actually be worthwhile, since the aesthetic improvement could be useful to future users, provided that no corrections to grammar or terminology are made.
Similar logic applies to "PSQ closures" (especially since they are more in line with the "on hold" language, in the sense that we hope they will be improved and reopened) and "unclear what you're asking" closures. In general, I would say that the only true waste of time would be editing the MathJax of questions that are sure to be deleted, such as blatent copies of millennium problems, questions that make absolutely no sense, spam, rants, and so on.