You are right about upgrades. That is the key to not only beautiful cities, but winning in War, as well as having an easier time with roads, and everything else. I learned quickly not to invest in water not because it’s not beautiful, but because you will need the money for upgrades.
upgrading roads WILL end! They can only be upgraded so far! One trick is to buy the Sakura Roads, which then never need upgrading. They can handle the same traffic as the expensive Vu roads.
upgrade War cards often. I wait for Challenge points to finish upgrades.
I’ve been playing since almost the beginning of the game, and I’m still not at maximum card level on any card! I don’t cheat, and I spend very little real money. This is the greatest game out there! Still love it!