Career Crossroad

Hi,
I started out with vb6, doing it for about 3 years, then moved on to vb.net/c# for another year or two.
Then got into web development using c# / asp.net for about 2 years, got fed up (for some reason open source just appealed to me more and more over time) and decided to switch to php/mysql, which I've been doing the past just over a year.

Due to always changing, and pretty much being self-taught, I'm not really good at any of this. I'm good at figuring things out, finding answers, deriving a solution from the business requirements, etc. So I'm doing ok, and all my boss now and before very happy with my work.

But I just feel I want to take a few months or more, and get really good at something useful. Something that can help me if my company folds, my future plans dont work out (I'm working on some system I came up with myself and hope to make something out of it).
Want to stick to web development, stick to open source, and stick to PHP / MySQL / Ajax as I got a solid and good knowledge of it.

But not sure....Start studying the php manuals like hell? Do the Zend Certification (heck, only about 15 certified zend developers in china, 10 working for the same company..that can be a selling point?)
Still not sure how useful, but started reading about this Zend framework also. Useful? Free? (Free is King in China, and I'm here to stay)

...sight...not sure.....got the time, got the brains, got the want....but not sure which way to go...