yes u can do it, in ur spare time and on ur local disk. i didn't suggest u to replace production code w/ urs, but just play w/ it a lot to fully understand it.

after reading all ur reply, I think ur problem is lack of practice. no matter how many open source side projects u put on github, they r just too simple/small/repetitive. u need to do bigger green field projects, either on a new job or in ur spare time. build something from scratch, write ur own library w/ advanced features like multithreading etc. develop application on top of it, test the crap out of it. like u said u r not the smartest guy in the room, u have to take lots of extra efforts to do well in this highly competitive field.