This is a more interesting effect anyway. The previous was basically a weaker version of Natives (lose 1 turn per crew).
The thematic implications of it hitting later on are better too. Instead of being stuck at the island longer, they sail along doing other stuff when they spot something in the distance and then spend a turn checking it out, only to find out it was unimportant.
Riches from Distant Lands: I could see this getting messy, regardless of the campaign game implications of sudden windfall riches. It sounds like it would force the next player to reveal how much gold they have. By “held”, is it just gold on their home island or does it include gold on ships, in forts/etc? Such a big reveal might change a game by tipping off other players if they should build a fort, flip Trade Route (UT from SCS), HI raid said player, etc.
I agree, this one would be a mess to implement because there are a lot of variables that would have to be considered, and a lot of specific details would need to be clarified. Getting to peek at another player’s entire gold collection is almost as powerful as the gold payout, but is only indirectly implied by the wording; it should be clearly stated as part of the full effect.
There’s also the issue of it being potentially game-breaking if a player purposely keeps it on a ship near home until as late as possible in the game, to maximize the value. It would be especially problematic in a timed tournament game where every player is allowed to have the same number of turns.
It would work better as a UT if the value was locked in when it was first loaded, and was based on something that was easier to determine at that moment, like the total value of all other treasure on the island where it was found, for example.
ADDED: Another alternative would be to add some sort of “poison” effect that forces the player to unload it as quickly as possible, because, regardless of how the gold value is determined, it could be a massive amount of gold value sitting on a single ship with no obvious downside.