I earn my living by selling my [old] knowledge. SO already pays me big by helping me replenish exhausted [old] knowledge, which in turn I can sell again.
I don't know if a-few-K-reputation person will agree with that, but IMO the site is a mental exercise - the stream of questions is flexing your jell-o like no daily job would - workout for speed, workout for fun, workout for heavy-lifting - your choice.
Another aspect that pays back big is the collective digestion of sickly complex concepts, that are pumped our way by countless number of employed brainiacs, that, among all the organic joy they get, need to self-justify their paycheck.
Having said that, if we want to spend our hours on SO and get paid, then what we need is an eBay for nerd merchants.
(Legal notice: By writing this herein, I have copy-right-ed this business plan and you're all under ND and non-compete agreements :-) )
(Real legal notice to "legal": I am kidding - please don't ban me from the site)