We could buy a pig with gems. Feed it food. When we need to food we could slotter the pig. Use stone to make stone Golems. A way to use the resource and have a new marching army. When needing stone we could disassemble or fight the golems to get stone back.
Or at a minimum being able to deposit gold into the bank and withdraw for a profit... Gold is so hard to come by yet more than half the game with research and allies depend on it!
I mean buying allies in itself is an investment. Each time one sells you profit gold, and if you get good enough at trading, you could easily make 250k-500k gold / hour with minimal work.