I had the opposite reaction, that it has not grown outside of its original niche at all.
Also, I think for some stackoverflow, it's not enough to tweak the colors.. Some of them might need a real disruptive tool to make it happen. For instance, the cooking one could have a hardware adapters to be used in the kitchen. Ok, that was a silly example, but I hope you get the idea.
Why would cooking experts or financial pros be drawn to Stack Exchange? They won't be. They'll stick to sites dedicated to those things that possess a very narrow focus, where the quality of content is likely to be higher.
It was an interesting attempt on Stack's part to spread out, but who really thought the end result would be them taking over every category?
Just take a look at Personal Finance / Money. That's a huge category that is very lucrative. Yet they're getting a whopping 5 questions per day for a three year old site, and a mere 7,200 visits per day. Why? Because "money.stackexchange.com" can never be promoted properly as a brand, it can never carry any kind of reputation as a separate product. An average person isn't going to buy into the notion that that site possesses authority on personal financial matters.
http://travel.stackexchange.com/questions/19941/one-foot-in-...
http://english.stackexchange.com/questions/1216/what-is-the-...
http://physics.stackexchange.com/questions/75459/why-do-chim...
http://skeptics.stackexchange.com/questions/17578/did-9-11-l...
I prefer if companies and sites focus on becoming the best in their area rather than continually pivoting to seek more eyeballs/profit.