It's become well-established that the purpose — or, at least, one of the primary purposes — of the "exact duplicate" close reason is to minimize dispersion of information/duplication of effort while keeping information easy to find with a wide variety of search terms.
Don't just take my word for it; Jeff said so (and he did it more eloquently than I did).
I used to be a pretty gung-ho editor, because poor-quality writing looks unprofessional, and I thought that that would harm the site in the long run. After all, what sort of experts want to hang around a place where people can't even figure out how to capitalize or use commas correctly?
I'm not so sure that's the right way to go anymore. Fixing incorrect or alternate spellings, and perhaps bad grammar, may make it harder for people to find the questions they're looking for using the sites' built-in search or the "Ask Question" page's title auto-search thingadongdong. Should we leave some or all "poor-quality" closed questions the way they are, to make search a little better?
Some points made in chat about this:
- this could be resolved by making search use all of revision history, not just current posts, possibly weighting the results to favor current posts
- this may be a non-issue for most people, who access the site via Google
- it may be helpful to have better spellchecking built into the SE engine