I think a better way for people to let you know that they want to register would be to have them contact you directly through an e-mail account that you could set up specifically for that. It would probably be a lot easier than deleting all of the spam that shows up in the Access Requests forum. It would also be a lot less nauseating for members who click the "view new posts..." link and see spam for things like father/daughter incest, before you have a chance to delete it. You could, then, just delete the Access Requests forum so that the spam will have no place to be posted. You could, also, make it read-only with a message telling people how to request access, if you don't want to delete it.
Just a thought.