That would be me...
Many of the suggestions would need coding. I don't really want to get into the business of writing and maintaining PHP extensions; I have enough other Freeciv admin to do as it is. Also, I've been trying to avoid much customisation, to avoid pain on upgrades (we're overdue one). I haven't found any trustworthy-looking extensions that look helpful; I've been a bit disappointed by the range of phpBB extensions, to be honest.
I was futzing around with a non-coding solution to limiting initial posts using existing phpBB facilities, but then the rate of the really bad hundreds-of-East-Asian-c*s*no-threads spam runs dropped off hugely, and it fell down my to-do list. Probably too fragile to be worth the effort really.
I did install the extension for http://www.stopforumspam.com/
a while back. It isn't super effective, but it blocks about half of registration attempts maybe? I think it's more use against traditional spammers than the specific c*s*no technique that's plagued us.
More mods> might be useful, but I don't know that any of the admin team are more likely to be around at the times I'm not (UK/Europe working day and night time). I'm generally on once a day, and can swat a spam account and all their posts in a few clicks when I do turn up. Apologies for the inconvenience in the meantime.