Nau spam (or maybe not quite spam, but a lot of them) can do several things. A fleet of Naus selling their goods at the other end of the planet. will give a lot of gold and xp for EACH.
But this seems to ignore the opportunity cost of building so many Naus, each for a one-off bonus and an irrelevant promotion (who really fights with caravels, or even ironclads, except to take on pirates?) You're getting perhaps a third of the unit's effective gold cost back in revenue - it may look attractive seeing your coffers fill up in one go, but that's a lot of production being ploughed into units you don't otherwise need - it's a false economy. How much would you get instead if you were building a bank in a gold-productive city instead of a Nau, do you suppose?
Quite frankly I'd rather have a Great Merchant (who can give you in excess of the money from 5 Naus from a fairly close CS) and take the minor hit to future GP production.
Remember, every Nau you build can do it. Also, the extra movement comes in handy for finding every civ first and founding the World Congress first,
That's true, and yet somehow I still failed to get there before the Shoshone in my playthrough. I think it's only on lower difficulties than Immortal that you'll feasibly get Astronomy before at least one AI (unless I'm playing especially badly), since it's a tech path they tend to prioritise. And if they beat you to the tech, the speed boost doesn't help (unless they only just beat you).
giving you a jumpstart on a diplo victory. Also, with extra xp, these can be good for protecting trade routes, which, in the late game, can become lucrative.
Just out of curiosity, what is your optimal way?
CS questing and pushing World Religion and World Ideology resolutions through (with support due to CS questing) (EDIT: And, above all, spies rigging elections). Gold is only useful if you want support from other civs, and to use when and only when CS offer you gold quests. This is important because CS influence from gold decreases after you've used it a few times, so much so that even the usual 'complete a project' gold quests are almost worthless after a while gold-spamming - "bankrupt" (the single gold coin quest icon) gives a fixed influence boost for giving gold, so this is always worth going for, but it's less common as a quest.
EDIT: An example from my just-completed game illustrates why gold-rushing is so suboptimal. I was going for culture victory but fell behind Korea, so turned to diplo late after not focusing on CSes or quests - leaving gold and a quick reassignment of my special agents as my only options. Money plus a coup took Mogadishu from Rome, who would otherwise have won the first leader vote, and I bought Riga, in both cases on the turn before the vote.
Come the vote, Siam stole Mogadishu in their turn, so I was behind both Rome and Siam - we all had enough votes to win, as I'd passed Freedom (bolstering me and, unfortunately, Rome, but not Siam who had the Forbidden Palace - I wasn't in a position to pass World Religion, although this is usually preferable), and missed out on the free votes for the next round; however the game continued because Rome and Siam were tied. The city-states went back and forth between me and Siam (I rigged Mogadishu, a coup took it back to Siam, my own coup gave it back to me) - eventually Siam bought both, but again couldn't beat Rome and the game continued again. At this point I was on 10 votes (minimum needed to win), the other two were on 14. With only two surviving city states and none available to liberate (the other two had gone to Venice), this only gave me one option: in 20 turns, take Sukothai (and hence the Forbidden Palace). This I failed to do because it was so far away, and the concurrent delays to the leader vote meant that Ramesses finished his spaceship the turn before the leader vote that would probably have given the game to Rome (as I had both CSes back at that point, although just before the end game notification I got a flag that Siam had bought Mogadishu again),
All I had was gold, and hadn't been building influence with spies nearly long enough to make my lead unassailable - had I focused on the Congress earlier I could have passed my religion or possibly become host. The gold costs themselves were money I could have better-spent on other things. The 'gamey' sanctions on civs stealing my CSes weren't available - Rammy was hostile towards me so wouldn't have been willing to trade his cash, and with no DoF couldn't give me his lump sum cash if I had anything to trade. I didn't have enough stuff to persuade Aiugustus to give me his money. I could have declared war on one or the other of them, but before the first vote it wasn't clear which of the two was my main rival - had I declared war on Siam, Rome might have taken the CS.
(if I remember correctly UB had scientist slot before nerf)
different gameplay.
