I have not found any reliable automated schemes. We fairly recently started using SpamBlacklist which stops some obvious types, but doesn't deal well with the form currently in vogue where the spammers seem to be trying to build a network of interconnected wiki/CMS sites all with spammy messages. If you do discover automated methods that work and don't inadvertently inconvenience the users I'd love to hear about them.
On WikiEducator it really amounts to having the community alert me when they spot something wrong, or just resigning myself to spending some time being "curator." I watch Special:RecentChanges, Special:NewPages, and Special:NewFiles for things that look out of place. I have (Python) scripts that allow me to delete pages from spammy authors (and block them). I also have a script that periodically checks new account creations for suspicious ones (such as varying the number of '.' in a gmail address to create a new account). Hopefully as WikiEducator grows, so will the number of people willing to be curators/librarians.
P.S. Yes, ham radio has been fun since I grew up in the central US, went to school in Boston, worked in Silicon Valley, Tokyo, and then Gisborne and now Te Anau. Interesting how different the HF bands sound from each location, although my prime interests now are satellites and software-defined radio. I also volunteer my services to provide system administration for NZART.
The only other way I had found to control actual links to the outside and to not be a convenience, was to build up a custom string of URLs you dont want and add that into $wgSpamRegex, but the effort involved in trolling the spammy pages and harvesting the links almost wasnt worth the time involved. Anyway, Ive been on a bit of a mission trying to find some answers and SpamBlacklist certainly cuts down the amount of manual deletions you need to do and thanks for the insight on how you manage this here.
I have a background in Radio, working at ZLB Awarua for the NZPO back in the day when they seemed to have their fingers in all sorts of pies, CW being my primary mode of communication! A rather outdated skill now :)