Uty said:
How much of an issue will balance be if it is available to AI opponents as well?
It's still a major issue, because what are the chances the AI has been taught to use these improvements
correctly? I've heard a lot of players comment on how the AI makes too many Cottages and not enough farms/mines/etc., resulting in high commerce and research but lousy city production. This looks to me like the AI isn't actually assessing the long-term effects of the Cottage improvement, but is simply assigning them a flat pre-determined value. So, what happens if you make Cottages better/worse? The AI probably would continue to build them in exactly the same way as before.
The balance issue is more a question of what sorts of improvements you should use. If you were to put massive bonuses on Suburbs, then the only tiles that should ever be anything else will be those that have a resource on them. The way I plan to get around this is simple: I'm adding several future eras, and so while Suburbs would be stronger than Towns, many other tile improvements will also be getting boosts along the way (similar to how Windmills and Watermills get stronger at Electricity and Replaceable Parts). For instance, once you research robotic mining technology, all Mines get +1 production. So, the relative value of the improvements won't change much.
Anyway, on to the other point: I suggested +1 production instead of more commerce, because a city with massive sprawl should be more productive once people in the suburbs can work in the core city, and you don't need more commerce. This way, in the modern era, you can pave over more of the earth for suburbia without sacrificing productivity. But as it is, Towns give +1 production under Universal Suffrage. So, maybe we should just accept that the modern "Town" already represents a Suburb... or, a Suburb under Universal Suffrage would be +2 production, the same as a non-resource Mine (unless you bump up Mines, like I mentioned above).