Sorry for not getting back to this thread sooner! I’ve just submitted my "ImageUpdater" component to the Extras repo, so it should be showing up soon.
At the moment it’s just a quick-and-dirty snippet I wrote to get the job done on my site, but it seems solid (my site has thousands of images and close to 2000 resources, many of which reuse images across pages) and it definitely makes the job of updating attributes painless. Hopefully it’s helpful to you guys (and others)!
If there’s enough demand, I’d really like to turn it into a Manager-based component with the ability to update other elements (links, for example), complete with file browser support for images and whatever other features people think might be useful.