I've been unable to find any button or link to show only the threads to which I've previously contributed, or otherwise selected to watch. Does this forum have such a function?

You can find threads you're watching in the UCP under Manage subscriptions. Handy links for your posts/threads are in your profile (e.g., bean74) under Search user's posts and Search user's topics. And you can do this with keywords and more with search by specifying the author/topic/post.