Just chopped two of the ghostly graves (in the market for gems) and got a spooky tower, A spooky wall, double the amount of haunted diamonds and a VERY cool looking Raven Atrium with at 22hr timer! Wonder what it will give me!
Edit - after checking, realized I got all of those decor items and diamonds from ONE ghostly grave!
Edit 2: chopped four ghostly graves and received: 81 diamonds, 3 spooky towers (have royal points!), the raven attrium, a Cownt Dracula cow, two baby widows (tiny spiders with unknown drops), 6 spooky walls, 4 songs of the undead, a raven lantern and a spooky gate! Totally worth the gems to me!