In my opinion, yes, you should approve/improve a suggested edit on EOL questions, or "questions that you know will be closed", but I wouldn't really put much effort like you did in that suggested edit you linked.
On a very broad perspective, I see editing a question as making it:
- Easier to read. This is done by correcting spelling mistakes. And,
- Easier to search for. This is done by correcting major mistakes like a wrong file being mentioned, or a wrong tag on the question.
Easier to read edits on questions that are closed/you know will be closed doesn't do much good, because it's eventually going to be closed. An example of this is the suggested edit you linked. As I mentioned, I would've done something else rather than correct those spelling mistakes on a question that will be closed. But to answer your umbrella question, yes, if an edit makes it easier to read, I would have approved the suggested edit.
Easier to search for edits are important because the whole point of AskUbuntu is to make it easier for users to search for old questions, so editing a closed/going to be closed question to correct a mistake should definitely be approved. People need to be able to find those closed questions.