I'm still getting comment spam, despite the posting timeslot idea. Obviously the assumptions I made there were unsound. So, here's the supplement that might raise the bar a little. If you want to comment on an entry here, you now have to enter a particular word of a well known quotation. If you don't or enter the wrong word then you get locked out for 10 seconds (a standard WordPress feature).
(code to follow if it's successful...)