We are totally on the same page.
Right now I put a dirty little link on my forumhome page with "Posts by email" in the forum description box for the forums that have email integration enabled but it looks very tacky so I didn't include it in the release til I figure out something better.
I was thinking either a separate page that lists them like you mention.
Or some kick ass way to note which forums people could do it on through an icon or something on the forum home page, that was super easy to understand. Clicking it takes you to the forum subscription for that forum
I'm so back and forth on how to make it more simple while still looking and working great.
Like the old saying goes... Keep It Simple Stupid