What advantage does contributing to Open Source give to a developer? Does it help in hiring? Does it help in building the portfolio? Does it help in earning money?
This "super" stuff makes it sounds exaggerated. It's just useful, it's not going to save the world (probably).
Does it help in building the portfolio?
It does. Many developers don't write public code at work, so open source is all you can really show off, other than your high school project.
Does it help in hiring?
Some companies value it, partly follows from the above, and partly because it shows interest with programming.
Does it help in earning money?
Also follows from the above, I think.
Some people place a lot of importance on open source contributions, others don't. When I'm hiring, I see it as a nice-to-have but I don't care if you don't ( I go into a lot more detail on this older question ).
Unless the job you're going for is specifically related to open source participation, it should not be a requirement. It will give you experience working on projects with remote developers; and if you feel your CV needs to be bulked up it can help with that.
But fundamentally I wouldn't devote a lot of time to it unless you enjoy doing so.
I gotta agree with Mark on the points below, I'm not a very much open source developer because I don't like the idea of code being 'too freely available' but if someone where to approach then i would help.
but I do think its a bit overrated when it comes into play with Github being open source, some employers like to check 'how active' you've been and how many 'commits' you're pushing. So you gotta be practically either doing your own code or helping on open source projects every day of the year :)