I typed an answer on my phone this morning, and while I did somewhat well I still made some typos. Then a wonderful soul came along and kindly cleaned up the mess I left.
Is there, or can there be, any method for upvoting an edit, or saying "This was a good edit"?
There are no points or upvotes for edits, no. Editing is part of the idea of community-maintained content; we encourage people to help make all the content on the site better when they can. The best way to thank the editor would be to pay it forward by helping to edit others' posts when needed.
Also, as JDługosz reminded me in a comment, users get +2 rep for each accepted edit until they earn the "edit" privilege. So lower-rep users do get a small rep reward along with the knowledge that they are helping to make Worldbuilding better.
If someone edited a post, you can use @Andon notation in comment. Just post a comment at him and tell him you appreciated his edit. That'll do. And personally I believe such comments to be a good thing to do, everyone wants to be appreciated.
If you want to show some extra appreciation, post an extremely well researched answer to his question, or set a bounty on one of his questions. Sure this might cost you some time, but that's exactly the cost of good substantial edit: time.
