Yes. Thinking about it, well, rather not. I mean maybe yes. Well actually NO.
Confused? Good. I am too.
First of all I would like to restate what I already wrote in the comments:
I know this is not the answer you are looking for, but I would never delete a question that has a valuable answer and I suspect neither jonsca nor Manish would do that. And I believe this should not even be a practise in SE at all. Valuable answers should not be deleted - at all.
If we establish this as the norm through this post, every future mod can be pointed to this (as long as the community does not revisit this practice) and will most likely act acordingly.
I have a serious problem with making substantial edits to very bad questions. They have been downvoted a lot. If you go about and actually turn the question into a good question, so that the answer still fits to that post, the downvotes will not vanish. New users will find the post with a -5 score and might think: "Oh, this is a nice post, but why was it so terribly received by the community?!" As a new user I (personally) would be a bit afraid to ask a question here.
Closed and downvoted questions with good answers actually show that we are a nice community and that we are still trying to help, even when it sometimes means bending our own rules.
I encourage making the post look neat. The contents of the post might not comply with our policy, that does not mean it should be horrid on the eye. They also should be categorised by the correct tags and the title should be as meaningful as possible. (Just have a before & after look)
What can be done instead of editing and reopening?
Disclaimer: This is my personal opinion - I am not sure this is the right way to go.
Once the post is in a preservable state, it could be locked:
This question exists because it has historical significance, but it is not considered a good, on-topic question for this site, so please do not use it as evidence that you can ask similar questions here. This question and its answers are frozen and cannot be changed. More info: help center.
But, when reading the following:
Posts should only be locked when something seriously bad is happening. A locked post cannot be changed in any way or voted on, and if the locked post is a question, no new answers can be added.
I gained some doubts, because the answer cannot be voted on any more, which is not how an answer to such a post should be rewarded.