Just noticed an enormous amount of spam on one of the images which was attached to a post. Seeing there's no option to disable comments on attached media, I quickly hacked a plugin myself to do that (and only that) only to realize such a plugin probably already exists.
And indeed yours fits the bill and is certainly more flexible, but the option 'disable comments on media files/ attachments' would be a welcome addition to 'inherit from parent post'. Any chance that could be added, so I could dump my quick hack? :-)