I don't think crystal rose emblems OR crowns should be handed out as island rewards. Just, doesn't fit. And in my honest opinion islands don't take "a lot of gold and AP to be high ranked." It just takes time, a lot of it. My island was rank one~twoish in all of the categories when they first came out and I literally had 80g and zero AP the entire time of getting it there before I got really bored of it.
I /do/ think there should be some reward however. Island skins or w/e perhaps.