I find that gold is fairly easy to come by as you progress in the game, and adding a single building to add +5 gildar to any city seems a bit steep. There are actually several techs in the adventure tree which spawn more resources, and merchants are a pretty fair deal at 1 gildar for 1 food. I wonder how many cities you actually have at turn 75 which are above lvl 3. Consider a single kingdom city with 2 gold mines ( a situation I see fairly regularly). Now, this city will make +10 from the gold mines, +1 from a merchant, +2.75 from the market, +6 ish from the trade center which is now around 19.75 per turn. If you decide to go crazy and add a bazaar and a mint, you get a 100% bonus and a 50% bonus. Maybe you add the palace and get another +7 gildar. Eventually this one city will be producing 40+ gildar a turn after 5 levels of gildar level bonuses.
(I could make troops, but they take forever to get to where I need, so I don’t)
If you are having trouble producing troops on the front lines, build some pioneers and build outposts near the front. While these cities won't have the resource numbers of your better cities, they can produce units as fast as most of your bigger cities can (including the time it would take to deploy). With these front line outposts, just get them to lvl 2 so you can build a barracks and have the population to rapidly produce groups of troops.