Great mod for reducing the infinite urban sprawl cities tend to become in the Exploration onwards. I do think it removes some of the fun of specialising cities though. I think there's a more balance friendly version of this concept in here somewhere - maybe more like your Better Bridges mod where a Brickyard will automatically become a Stonecutter once you get the right tech, but new cities will still have to build a 'Mine enhancer' building before they get the effects. Or even have obsolete warehouse buildings lose their tile enhancements completely on era swap, but the exploration age one gives +2 prod to mines, the modern one +3, etc.
