A lot of the spam diaries are persistent repeats of the same stuff, and killing them is a bit like playing whack-a-mole.
Maybe the site could do a similarity check against past banned diaries, with close matches requiring a positive endorsement from a trusted user (out of 50 or so randomly chosen) before it goes live.
That would trivially block a lot of crap, and accidental spam-blocks would still soon be overridden, while only a few TUs would occasionally be pestered to allow something to opt-in.
Just a thought...