Github allows for people to discover projects to be passionate about that they may not have discovered otherwise.

Before Github, the primary means individuals discovered projects was just by stumbling upon random websites... often times ones that hadn't been updated in who-knows-how-long.

Github clearly shows the health of a project by providing at a glance how long ago the most recent commit was, how many people have contributed to the project, how many people are "following" the project, how many contributions via Pull Requests are pending, etc.

I think that given the popularity of Github, there is a good chance of finding serious contributors.

i wouldn't call them "peripheral" if they have in parts led to a fork of the project already (See discussion of of vim contribution process and it's pains otherwise in this thread)