Transformative left-nav
It would be transformative for regular users if the left-nav gave users customisation options such as by adding their own links etc., e.g. for meta, favourite chat rooms, the ability to pin questions by dragging them to there, the things they use most. Then it would become a joy to use.
Failing that it's at least be better the user has the ability to hide it, as it fills a lot of prime real estate with empty white space. But it should be clear on it, that it is, by some pin or x in the corner, rather than hidden elsewhere.