Please consider adding a quest along the lines of "Accuumulate xxxx crystals of Adamantium via adventuring" with the reward to be a Crystal Tree. It could be blue (the same blue as the adamantium) and when you poke it (like the raving rabbid) it could make a wind chime sound. In our discussions we made it require quite a bit of adamantium, like 1000 crystals. They don't provide anything except beauty to the island, so they won't affect the economy except to add some value to the useless blue crystals we are all dusting weekly.
Best regards, JuliaVZ