Don't know how hard it would be to do, but if the software could be programmed to soft delete all posts by any user given the "spam bot" infraction, it would save quite a bit of time, since mods would no longer have to "search for all posts by Spambot43" and delete each one. And since spambots usually start threads rather than reply to them, doing this would in most cases wipe the board clean of all traces the moment the infraction is given. Just an idea.
This is coming in vbulletin 3.7, as a built-in feature Mods will be able to simply check the box next to a spam thread, and click "delete as spam" - this will ban the user, wipe their posts, etc.