How much gold does a diplomatic mission provide, and is it worth it?

The money gained from performing a diplomatic mission is 350 + (50 * <era number>) where era number is just a serial number starting with 0 for the ancient era. In addition game pacing also affect this number: quick games modify this value by 0.67, epic by 1.5 and marathon by 3; or in other words:

             Gold in   Gold in   Gold in  Gold in
Era          Quick     Standard  Epic     Marathon
--------------------------------------------------
Ancient      234.5     350       525      1050
Classical    268       400       600      1200
Medieval     301.5     450       675      1350
Renaissance  335       500       750      1500
Industrial   368.5     550       825      1650
Modern       402       600       900      1800
Future       435.5     650       975      1950

I know of nothing else which can affect the gold amount.

Now, if I have a strong economy in the late game I typically gain another 100-200 gold per turn when in a golden age. That means that the only way in which a golden age is preferable to a diplomatic mission is when it lasts at least 3 to 6 turns. But usually by the time I get to the late game my golden age duration from great people is really low, and if you take into consideration that the influence gained is worth a few hundreds in itself, you'll see that a golden age looks less and less profitable in comparison. All this is especially true if you play in longer game speeds, which translate to higher gold.

Of course, golden age also nets production, so it's still a dilemma; but I do believe merchants are worth it from the financial aspect.