My understanding is that the +50% caravan gold bonus doesn't work at all. I know it doesn't work on found caravans. I haven't done the math on built caravans, but others have and have reported there's no improvement. Building caravans is useless anyway.
The Spanish bonus works. It refers to great lands, you know when you name a river or a hill or something. You get double gold. Early in the game that means you get 20 instead of 10, which is enough to rush a warrior. Pretty nice if you're out hunting for whales and instead find an empty cap.