I think that developers and companies will benefit from this as much as the open source community will. One of the best ways to get better at coding is to read other peoples' code, especially well maintained open source code. Whether you pick up style tips or best practices from someone else's work, or sharpen your own eye by figuring out how you could have done it better. Analyzing an open source project is also great for learning a new language or familiarizing yourself with a new programming paradigm. In many ways this is equivalent to telling your employees "Spend two days a month honing your skills in a productive way".

I would definitely do this whenever I wasn't rushing to meet a deadline or dealing with a full bug queue.