While I disagree with your opinion on it, I very much understand your reaction to Elantris. It is certainly a story that benefits from a re-read. I would advise re-reading it with the mindset that Hrathen is the hero of the story from the beginning; I suspect you'll find it to be quite a bit more interesting.
Regarding Cosmeric relevance, In addition to Hoid and Galladon; I would focus on the sculptures and such in the room that leads to Devotion's perpendicularity, this was our best source for Worldhopping for quite a while. Also the Realmatic implication of the Dor is very interesting. In addition, Hoid's failed experiment in the epilogue gives some interesting clues regarding identity and how the Shardic magic works. It also is a decent indication of Hoid's lack of understanding regarding Identity (at the time), if he had a better understanding he would have known from the get-go that it would not work.