How does one balance closed source work while maintaining a "public" presence in the open source world. Time is so limited and splitting focus doesn't seem like a good plan.
If you are working at a small company or startup that is using other open source projects/products, you can contribute to those projects to help improve your company and get paid to do it.
In the end, if you are hacking on something you think is neat or interesting, put it out there. The worse thing is no one notices, the best is you now have things you can point to.
Personally, I use a combination of all the above, yet I am the first to admit, I screwed up early on in that I used a company email/GitHub account I had to do most of my contributions instead of my personal email. Had I used my personal it would have made my contributions easier to track, but either way they are provable.
Either way, the more you put yourself out there the better. Good luck!
But it does pre-suppose that you like to dabble in writing code in your "free" time.