Personally, I don't know that such an undirected contribution is really what the community benefits from. I personally believe the best module writers are those who work intimately in the problem space they are dealing with, and the best people to add to an existing module are those who know the module intimately.

My recommendation to programmers looking for ways to contribute is to find a problem to solve or a software project to join directly. In the process of working on that, you'll either use some modules well enough to see where they need to be improved or else will wind up creating something that others can use.