Earlier quoted context omitted.
If you incrementally add one new feature then any existing user may or may not use the new feature. But what happens if you radically overhaul a site, changing its style, changing the items, style and placement of the navigation and improving but changing core functionality?
Can you not throw away what's bad and keep what's good during your overhaul?...
It's generally really hard to throw away stuff, even if it's bad. Users get used to things in the UI even if it's bad.