Interwiki links are incredibly helpful to navigate when you're doing a task that requires the same page on multiple wiki's.
It often happens that I want to switch between two wiki's and their special pages. That usually means I first have to figure out the English name of that page, then go to the other wiki, and type in Special:EnglishName .

It would be very helpful if we could get interwiki links on special pages (especially Watchlist) to all wiki's where I have an active user account (or a self-specified subset thereof).