Thanks for all the feedback, you've been super helpful!
I definitely feel like I need to increase the rewards for completing the treasure maps. They take awhile and don't scale with your fleets cargo hold which I completely overlooked, once you get ships with more cargo capacity its not even close to worth it. I'm not sure exactly how I'm going to go about it but the treasure map voyage will def be greatly buffed in an update soon.
Expect more regular updates soon!