A tempting proposal
On the one hand, this is very appealing - those answers are annoying. Of course, so are non-answer answers posted by such users on questions they don't own, which is at least as common and something this will do nothing about.
On the other hand, this locks new users out of a valid and accepted means of using the site. It breaks a SO feature for these users simply because other users have misused it. As Pollyanna also notes, SO already tries to discourage users from answering their own questions, suggesting the use of comments instead - of course, some ignore this...
Proof of the problem?
It would be nice to see some evidence that this solution has at least a chance at working; some data as to which rep levels have the highest occurrence of self-answering would go a long way toward demonstrating the scope of the problem and provide a good tool for choosing the right rep-level for the cutoff (my gut feeling is that even 100 points is unnecessarily high).
Encouraging desired behavior
Normally on SO, comments are intentionally discouraged in favor of posting answers: when viewing questions from other users, a SO user will see a great big big "Your Answer" entry field and only tiny gray "add comment" links. And new users don't see the "add comment" links at all on answers to questions they don't own...
So perhaps a better solution to self-answer non-answers might be to similarly encourage new users to post comments on the answers to their own questions by showing the comment entry fields instead of tiny gray links, while keeping the self-answer entry field hidden: