I think working on open source, both unpaid and paid, projects definitely has been worth it for me professionally. Independent of self gratification and such (rather important IMO), it has lead to offers for interesting jobs and by that increased what kind of remuneration I could get. Above what I think the additional years of experience themselves would incur.

I think it's harder to answer that on the angle of open sourcing projects. I've, together with colleagues, spent the last few years doing paid for feature development for an open source projects. It's possible to have a company around that and support, and grow. But it's not easy.

My impression, more from the side lines, being a technical person occasionally involved in sales, is that it help in lead generation, but that the conversion ratio tends to be lower than with leads for a closed product.