I have recently seen this question, where I see a spelling error in the title. I wanted to edit that, but I see that question was closed already. I am a bit confused to edit that title. Because editing that question will bump that on the front page. Should I edit that title or I should simply leave that question?
In my opinion:
It is OK to edit closed questions, though sometimes you should be more reluctant to edit them than you would be to edit open questions.
Preventing them from being bumped up to the front page is not a major reason to avoid editing them--since there won't likely be additional activity, they won't stay there for long. If an edit is worthwhile, it's worth having people see it and be able to react to it (even if they probably won't).
Whether or not an edit is appropriate depends in part on the question's close-reason.
Closed questions with formatting problems that can be fixed should be edited.
Closed questions that can be fixed for reopening, while remaining useful to the OP, should be. That is, if you know what the OP meant to ask in a question that was closed because it was unclear, go ahead and edit it. (A trivial example of this is if the question was closed as not-a-real-question, and the OP accidentally enclosed parts of the question between
>, hiding them.)
Closed questions should not be edited to generalize them, especially if they are closed as too-localized, unless you are the OP or are editing the question on behalf of, or in response to a discussion with, the OP.
Closed questions with spelling or terminology problems that can be fixed should be edited if the problem is sufficiently bad (or if you just really feel like doing the edit), unless they are closed as a duplicate of another question. One of the reasons we keep duplicates (rather than eventually deleting some of them) is so that people searching for the same or a similar problem can find them and be directed to the master question, even if their search would not have revealed the master question otherwise. Keeping misspelling, and wrong terms, facilitates this goal.
To expand on the idea of retaining misspellings:
I think we should really keep misspelled words in closed questions. Common misspellings of "terms of art" (like "Ubutnu", "Foxfire", and "patritioning") may be the most important situations to retain misspellings, but we should at least seriously consider keeping even misspellings of common words. A question about how to "clere Firefox history" will help someone else who makes that typo, with minimal disadvantage since a correctly spelled query would probably find the master question or another duplicate.
On the other hand, I do agree that misspellings in lengthy prose that are unlikely to match even mistyped search terms can safely be corrected. Misspellings in titles of dupe-closed questions, in my opinion, should virtually never be corrected. The only major exception I can think of is if the OP decides they want to correct it (we should respect that, though not encourage them to correct it), or if the misspelling would reflect in an unjustifiably negative manner on the OP. (For example, the OP may have unintentionally misspelled a word to convert it to an offensive word. In that case, they would probably prefer that the misspelling be corrected, even though doing so would decrease the success rate of subsequent searches with the same misspelling.)