First off, I apologize for the recent SPAM issues. Last week, I performed a full upgrade of multiple services on my server as well as updating this forum to the latest 1.1.x version. I also disabled the registration captcha that hasn't been working correctly for more than a year. Since then, I have enabled the use of recaptcha, added 2 "human verification" questions, and have added a few checks to the forum code to be on the hunt for spammers. Sadly, spam is still getting through, though I do have a few more countermeasures I can deploy.
As for your notify request, I have looked through various mods for SMF and haven't really found something that would do what you wish. SMF 2.x does have both daily and weekly notifications, however that is still in the release candidate stages and if we migrated to that version, we would lose a lot of existing mods applied to the forums that make life easier. I could have a look at the code itself and attempt to find out how easy it would be to add such functionality, but I am really lacking on time lately. SMF's code isn't the cleanest either...
If you have any suggestions on some methods to try to help catch more of the spammers before they register, I am all ears.