Might I suggest actually deleting the SPAM accounts and not just blocking the IP or deleting the related posts. 

For a spammer account here is what we do (on other sites) to ease SPAM posts. 

-Delete all posts (removes links current and any future ones) One trick used is to make a generic post with no links, then come back and edit the post later but with added SPAM and links. This can go un-noticed for a long time.  (Only allowing post edits by paid members can help here too)

-Block the IP (Many spammers use the same IP for multiple accounts)

-Delete the USER. Spammers often use auto account creation with password savers. Deleting the account makes them start all over and will often be more work than they will bother with. It also completely invalidates the site to any scripted/automated tools being used to post SPAM. It breaks their scripting and this can free the server from having to service automated post attempts because they can't even login. 

If for some reason we don't want to delete accounts, limiting a brand new user can help. ie Only allow posts to the Introductions and/or emergency forum. After an intro post or some other valid attempt at site use, a new level of user can be applied. You could also move an offending party to a group of shame and label them as spammers that have no posting rights. This is better than nothing but the server may eventually have to contend with dozens or even hundreds of post attempts from these "valid" accounts as they continue to login and attempt to post.

Anyhow, thanks to the Leadership/Mods for the effort keeping the site cleaned up. It's a frustrating, thankless, and often unnoticed role.