[[Special:AbuseFilter/21]]
For the little that my opinion is probably worth, I would find it confronting and unwelcoming if I was an experienced wikimedian and was unable to create a user page at a new wiki, especially as it is one of the first things that I do at a wiki. Noting: It would be expected practice that stewards, global sysops, and global rollbackers have user pages on wikis on which they operate I perfectly understand the issue of spam and abuse, and have written filters to assist in the wholesale management, I just do not believe that this particular filter is the means to progress. If you tied it with something like a test that had & added_links and it gave a preliminary warning of what is expected, only then would I see that a DISALLOW was acceptable. I would also think that if someone was using a template like {{soft redirect}} or {{softredirect}} with a xwiki link that they would not get caught either.
With regard to abuse filter help, I can tell you that your checkusers have been offered filters through the checkuser community. Further any of your administrators who hang around in stewards' IRC channel should have heard the offer as it has been made, and I know that I have personally added some of my filters around the wikis.
I have been presumptive and gifted filter 23, though only set it to monitor, rather than do anything.
It's not without reason that en.Wikt is regarded as the grumpiest wiki... :P
To be fair, I myself have created brief userpages on other wikis after only one or two edits to them, so I can see why visitors to this wiki would want to do the same.
I note that filter 21 has caught a lot more edits (which appear based on their systematic usernames as though they would have been spam) than filter 23, though, i.e. filter 23 may have a low rate of false positives, but it also lets through a lot of crap.
Is there a way for a filter to check not only how many edits a user has made on this wiki, but how many they have made globally? Then we could block users with fewer than, N edits globally, and catch the spambots without catching global sysops.
Anyway, we should probably be having this conversation in the WT:BP rather than on CodeCat's talk page... see Wiktionary:Beer_parlour/2013/July#Blocking_new_users_from_creating_userpages.