Kevin,
Can you check whether SMF supports something like
VBulletin's "Spam-o-matic"?
I am a Moderator on an Indian FIAT Forum and we got much relief after we installed this plugin for the forum. Now its automatically scanning posts for spam and most of the time it sends away spam before it can get an opportunity to show up on the forum. Sometimes it gets overenthusiastic and puts user posts for approval by Moderator if it contains a link but it's a small price to pay for the overall quality of the forum.
Regards,
Sunny.