You need to normalize by subtracting the 2 food cost from each tile, but that adjustment is irrelevant for tile-per-tile comparisons. e.g. this adjustment says the farm is 1f 1c = 8c and the gold is -2f 3h 9c = 4c, so its still a 4c difference. The big thing this overlooks is that if you are spending any time working at the next larger size, getting there sooner is worth extra yield. (making the farm even better) --- Regarding commerce vs. wealth, 1 commerce = 1 gold is the right thing currently, since there are no markets/etc: i.e. any gold not covered by other means would be covered by the slider which converts 1 commerce into 1 gold.