My most advanced cities are now in the Dragon's chapter & I have not upgraded any MA in any city. I never felt the need to & it hasn't affected my game play over the last 3 years. My elders who started before me seemed to all be in consensus that a 3rd builder was the best diamond investment in the game. Many of my cities took advantage of the free builder with diamond purchase as well. When I saw the benefits of the 3rd builder in these cities, that is when I decided to save up & get one for each city. I learned early on here in the forum that magic residences & workshops were poor diamond investments, because in a few chapters, they become obsolete, so I didn't buy any (I have one residence that was given after an FA glitch). After each of my cities had a 3rd builder, I saved my diamonds up & have occasionally purchased expansions. A few times, in a moment of impatience, I have used diamonds to finish off a production or upgrade, but kind of regret it afterwards. Thankfully, when the Wishing Wells were first offered, I obtained multiples of them & I have only been placing one at at time. Every 100 days, I swap out the expired one for a new one. This extends the time in which I may obtain more diamonds from the daily gifts it gives.