Any sort of control would do. The spamming process is inevitably automated and always easier for the spammers than it is for the cleaners :-/
Personally, I'd be in favour of locking down the object library for now. As no-one is contributing, this wouldn't be an issue. If people do have things to add, they can request an existing user/admin to give them an account. This would be a perfectly reasonably stopgap in the mean time.