There are on average 5 a day. Sometimes 1, sometimes as many as 10. I couldn't read the higher CAPTCHA settings myself, so I'm going to keep it on medium (level 3 of 5). It's probably mostly humans making the accounts anyway, as people have noted. It might be easier to bump into the spammers in GD and DF GD (I usually get multiple reports on those), but they show up in all of the sections (a lot at the top board with the DF release announcements). I guess it's starting to bother people, especially when they come on when we're asleep, but it isn't a huge problem for me in terms of time. The total cleanup takes maybe 15-20 seconds per spammer, since there isn't really any investigation or thought necessary for the vast majority of them. The only trouble comes when I have to delete a 100 post thread people have been playing in a bit too much, since that 504s the board for a minute. or when an enterprising spammer jumps in with 20+ posts.
I don't think messing with IPs would help much -- I just checked the last batch of spammers, and they all come from IPs that had never been used before. I've banned a few blocks of IPs in the past that were being heavily abused, but I'd rather not go to that too much, since we have people interested in B12 all over the world and they can get caught up in IP bans. There are a few email domains that seem to be spammer-only (psiek.com?), but I don't know much about that and which ones are okay to trash -- many of the spammers come from gmail accounts, for instance, which I clearly can't block.
I don't have a lot of control over nuanced tweaks to the forum, as far as I know. All I do with spammers is ban them and delete their posts. Those are heavy moderator powers to hand out -- and if the new moderator didn't have those powers, it would still be the same amount of work for me (and more, because I'd have to manage moderators).
So I'm not sure I have a lot of options. At the same time, this is not a huge time sink for me. One trolly/flamey forum spat takes up as much of my time as 50 spammers. If it's the unsightliness of it rather than a concern about my time, then it would probably be best not to bump spam threads, but I'd hate to make that a rule, since there'd be more people yelling at other people over breaking the rule, rather than the generally harmless goofing around that happens in to-be-deleted threads now.