I think it would be a real shame if BBC Four ended up closing. I'm in my 30's, so not in target age range as suggested by a lot of media articles, but I love all the pop culture and music documentaries, TOTP repeats and other archiving programming. In fact it's probably one of my most watched channels.
It's a wonder really that BBC haven't pushed their 'BBC Archive' brand a lot more, move all the history docs and music coverage onto BBC2, and then focus on repeating old shows on BBC Four. Not the stuff that gets non-stop repeats like Dad's Army and Only Fools, but stuff like TOTP, maybe Blue Peter, Tomorrow's World, Play for Today etc that don't get seen so much!