Unfortunately you cannot refresh all widgets whose keys match a certain wildcard. You can only refresh all widgets * or do the trick that the scrolling post stream does there with the dirtyKeys if you know the ids of things you are changing.
Your solution of the appEvent in the parent component with the keys should work. I think a cleaner solution would involve re-engineering Discourse’s widget code a bit to add wildcards, or refreshing a widget by name instead of key.