Editing is at the core of good Q&A, and one of the things that moderators do before migrating any question is to make sure that it's the best quality possible so that they don't dump garbage onto another site.
Thus, closed questions, including off-topic questions, can and should be edited and improved. Not only does this make them more visible, but it makes it easier to judge the content for the content itself, without all the noise from spelling issues, language barriers, and poor formatting. This ensures that a question that should be migrated will be more likely to get migrated by busy moderators who may only have a few moments to glance at the post and make a snap judgement.
In a broader sense, it's a good idea to edit any question that contains these sort of issues. When you clear out the cobwebs, it becomes much easier to tell if the question is constructive, loo localized, not a real question, or if there is some helpful comment you, or someone else, could leave the asker to help improve the post. For the same reasons as in the migration example, editing out the distractions makes it much easier for the community to make a fair judgement of the post.
In short, if you see a suggested edit that substantially improves a post, just give the question the benefit of the doubt and improve it. Hope this helps!
Lastly, I believe the inability to close questions in the suggested edits queue is status-by-design, as the Stack Exchange team feels that reviewers should focus on one thing at a time. Instead, users navigating the close vote review queue will likely have this covered for you. ;) Also, consider that when you approve the edit, the question bumps to the top of the main page, where it will be seen by countless Stack Exchange users, many of whom will take action if they agree the post should be closed.