Sorry for reposting, (sort of like regifting!) but I made this comment at the end of a dying thead and was hopeing to get a bit more feedback.
I like the idea of towns/cities not having to follow specific pathways or upgrades as they mature. For instance, maybe one small, centrally located village could have the strongest walls and best defence- in times of war, maybe most of your people would flock to this town (a storehouse of food could be kept here as well). Sure some outlying town might get sacked but with the populance mainly intact, rebuilding may be fast. This might be a viable option for some types of gameplay. Another example-having a centrally located hospital, even if its in a small town, may impart some benefits to nearby larger town, negating the need for each of then to build their own hospital-but also making that one hospital more valuable to defend. Having town rely (at least in part) on building from other towns could really add more strategy to town placement, make town specialization more viable and interesting, and impart the sense of your nation really working together (rather than independant city states-which you could still build if you wanted). I like the idea (and others seem to agree) of having a town really good at farming-producing most of the food for the kingdom, a well defended-but small-trading center, a small town in the mountains that can take advantage of some magic source and specialize in being mainly a magic training center, and so on.
So when we think of buildings- would it make sense that at least some of the benifits derived from them effect nearby towns in some way-so that absolutly every town does not need a grainery?
-Towns within 10 tiles or 10 movement points for a horse (an attempt to represent around 1 days travel)-If movement points are used this automatically takes into account roads, terrain, and bridges. This makes bridges and roads more stratigic.
-if movement points are not used the standard distance can be modified by the presence and quality of the roads, mountains and marshes slow travel.
-the type of government could also effect the strength of this relationship and give you a real trade-off between building a nation and a series of city-states.
-If a city is underseige these benifits are lost (unless there is an option to build some sort of secret tunnel out of the city)
Some more examples:
-hospitals- towns within range have faster headling rates, plagues or other diseases has less of an effect.
-Grain silos- keeps nearby town from feeling the effects of a famine
-stronghold - (as I mentioned above) could save the population of nearby towns even if those town are sacked.
-Universitiy- nearby towns all produce research at a faster rate.