Which brings up an interesting point, is it possible for *anyone* to be 100%-ass at *any* language?
Oh, sure, every community has its 'gurus' ... but even if you spend every waking moment mastering your chosen 'school of thought' the wheel keeps turning and inevitably your goal becomes a moving target.
If you want to become a master of the English language, why study English exclusively? English is changing subtly and overtly right from under us (jargon, slang, cultural trends, values)
You may benefit more by comparing it to Esperanto, French, Arabic and Japanese ... comparing differences helps you see the forest for the trees.
No matter where you go in the world, you can never know *everything* about a given city, so why not try to visit a new one each year, and take some souvinirs back to the place you call "home"