I just played the first half of a game as Spain, king, continents, standard size map. I spawned on a long loopy island with only Egypt and luckily a couple of city states, one right near my capital with sri prada. I built up a few archers and warriors and took the city state to get a supertile- it has grew bigger than my capital by turn 120. I then dropped two other decent cities to help push my science and speed up exploring the world. Askia was alone on a nearby big continent, complete with a CS with the great barrier reef. I took them out with archers but it took forever. I just got galleases ready to help when it fell and made two supertiles. One tile of the reef was on coral so it was even more over the top. I have since found a few other CS with natural wonders to capture soon and see how powerful they are. I currently feel like double yields are just about right. I got the pantheon belief for extra culture and faith on natural wonders too, but given how distant CS with natural wonders tend to be, and the religious pressure from all their neighbors, I think this pantheon is actually very underpowered as it is. Maybe make it also give double happiness from discovering natural wonders to augment the exploration theme? Haven't gotten to missions and conquistators yet....might be a while before I get back to this game so I can only really comment on the UA.