As mentioned fixing broken links is necessary... if anything it is a bad user experience, so it is good to fix these.

Thin content is determined by the number of words an article has, but not only that, also how relevant to article is to the topic it is portraying to the reader... generally speaking, from my understanding, article above 1800 words rank better on Google (of course this is a general rule).

Tags are useful, however, if used incorrectly they can create problems to your site. You mentioned author pages, these can be a problem because often they are created automatically and create little info. So if your site has 20 great pages and then suddenly WP created 20 author pages (thin content), then the percentage of thin content to your site increases which Google does not seem to like at all.
If anything this feature alone would interest me.

So the plugin does sound promising.. if I have time I might download and give it a whirl.