Lunesse, perhaps one way to slow down the spam would be to make some people Moderators?
I'm a Global Moderator on another forum with 3500+ members, and the Admins simply wouldn't be able to cope without the help of us moderators, who are able to delete/lock spammy topics.
Just some food for thought, thats all. Especially considering how these forums are growing in size on a daily basis, you might want to think about picking some of the more active members to be moderators, and help you out.
I wouldn't recommend me, however. I'm hardly here, lol.