Here's what I learned today.
Under My Stuff | Edit Preferences, there is an option "By default should anything added to your Watch Lists be emailed to you?"

Once I've chosen "Yes" and then make a thread "Watched", any subsequent posting shows up as an email in my inbox.

I think it's been there all along but I never knew about it and just grumbled to myself. See? Another thing learned: Grumble out loud and maybe someone else knows the answer!