I'm know I'm not the first to say this, but the rewards need improving. I know this game is supposed to be something of a grind, but It's becoming less and less rewarding, especially at higher levels where you need to work more but the reward is about the same. On top of that, with the difficulty bumps, you remain on islands longer making you a target. Which is understandable, but I think the rewards should match the risk.
Here's how I believe the reward system should be tweaked:
-Castaway Chest: 150g - 250g
-Seafarer's Chest: 250g - 450g
-Marauder's Chest: 500g - 700g
-Captain's Chest: 750g - 1000g
-Admiral's Chest: 1000g-1250g (I know this doesn't exist)
-Cursed Chest: 1500g - 2000g
As you can see, I hope for another non cursed chest (Admiral Chest), and since the cursed chests are a pain in the a$$ (especially Chest of Sorrow for solo players) I think the reward should be more suiting. I also think they can build on different levels of Cursed Chests that range in difficulty as you level up (and also vary in reward, but starting at 1500g).
Clearly I haven't touched on Cursed Skulls or Merchant Items (I'm ignorant of Merchant Items since I don't play those quests) but their equivalent items would value for about that same. Also, this may already be a thing so correct me if I'm wrong, but there should be Magical Skulls that affect you similar to Cursed Chests. I also think there should be magical skeleton bosses you'd have to fight for them.
Let me know how you'd want the rewards to be structures.
