Suppose your favourite module is CGI.pm. Ovid already described its coding quirks before. Would you learn something from it?
Would you learn nothing from it? You learn something from absolutely everything. Spend less time lazily debating if it's worth it, and spend more time actually doing it. I have yet to meet a successful person who sits around going "hmm, should I learn this, I wonder how it compares to this..." Stop looking for reasons to avoid challenges.
And if you would learn something from it, would it be considered "good" by current coding standards
It doesn't matter whether the code is "good" or not. As long as you keep an open, objective mind you'll learn just as much, if not more, from it. If you can't handle "experts" telling you flat out lies, if you can't learn to prove things for yourself, find a different hobby.