What I'm hoping for here is that the luxury resources traded away by the Dutch still count as luxury resources they have (like the happiness listing would indicate) - trade route gold gain is partly based on the amount of different luxury resources you have, it seems, and that might be a small indirect buff to the Dutch trade routes.
It doesn't matter whether you are trading the resources away or not - it's not the resources you have that get the Resource disparity gold bonus, but the improved resources within the cities (the one you go from and to).
In other words, you know how, even if you trade away your last Gold, you can still build a Mint in the city that has it close-by? This is exactly the same.
For a more in-depth look, let's imagine this scenario:
You are playing as Greece, and you have the city of Athens with Gold, Wine and Iron. You also have the city of Sparta with Silver and Copper. The AI is playing as Japan, and in Kyoto, it has Gold, Salt and Horses, while it has Citrus and Spices on Tokyo.
If you made a Trade Route from Athens to Kyoto, this would have been the resources you'd get bonus from:
Wine: 0.5
Iron: 0.5
Salt: 0.5
Horses: 0.5
You would NOT get the bonus from Gold, because both Athens and Kyoto have Gold in their radius. You would NOT get the bonus from either Sparta's or Tokyo's resources, because you are making a Trade Route from Athens to Kyoto. This bonus would maintain even if you trade away your last copy of Wine, because you still have Wine in Athen's radius.
Hope I made sense!
