On the Haunted Wreck:
It holds Two Major plot elements of import for the Iron Gods adventure path
1) The Inhibitor Facet: Can be used to hinder Hellion and goes toward shaping an Iron God far further into the campaign.
2) A recording offering additional clues regarding the final conflict upon the ark-ship Divinity... and the name 'Unity.'
That said, beyond it being a possible side-quest perhaps suggested by Redtooth, there aren't a lot of hooks pulling them to the Haunted Wreck if they aren't inclined by the fact that it's there.
Anyone have any ideas of ways to nudge them into that spooky valley? I already have Redtooth promising them high explosives to blow up the Receiver Array if they can rescue her brother, so I'm slightly hesitant on leaning too hard on her as a quest giver; especially since I don't know what her motivation would be in having them bust ghosts.