I built twice as many diplos at that single point in time by knocking off four envoys just before Industrialization, building each in one turn. I'm not sure I'm better off saving my gold (see below), but... I do follow your reasoning, and know this is inefficient. In the two games in which I recently happened to stockpile and promote envoys, I won a DV going away. I did this the obvious way: building a tech lead, beelining for Telecommunications, and preparing to fight last-ditch wars. (I said all this above.) I had gold coming out of my ears at Industrialization. I only got low when I promoted my fleet to Destroyers and Battleships. This is standard for me in a well-played Carthage game. So... How could I have spent my gold to reach that tech faster? I rushed every science building and picked up every science Wonder. Building a bigger military? Mine was more than big enough, given that all I needed was a fleet on two oceans to head off AI navies, and mine was both the best-promoted and most advanced (almost always one level ahead). It was pretty much whack-a-mole until Telecommunications (as it often is with a good Carthage game, where I conquer/vassalize my continent before meeting the other). Do you really think I worry about promoting envoys? If there's one area that could always be better buttressed, it's happiness, especially when I'm being steadily dogpiled. I actually feared running out of gold due to that. But often the answer to brief unhappiness was switching to Wealth — and guess what that did to my income.