I'm not sure if anyone else would agree with me on this minor subject, but I'd like to see roads be costly, with fairly formidable benefits. In most games, roads generally don't cost the player very much, and building them is often times one of the "low hanging fruits."
I'm thinking that perhaps roads should be a much larger strategic and economic consideration than they have been before (aka. much more expensive and more valuable.) Sure dirt paths would be cheap and probably pop up on their own, but stone or paved highways would be very, very costly with very large benefits. Not only would you get the usual trade bonuses and movement bonuses, but you would also gain other critical benefits. For example:
1. Greater loyalty in non-capital cities, due to greater exchange of ideas and cultural commonality.
2. Greater influence of your prestige in foreign trading cities.
3. Increased relations boost if you sponsor a better road into a friendly trading partner's territory.
4. Development of small-scale townsheds along roads which rely on the local essence imbuement from a neighboring city. They provide a small boost to empire income and research. They would start out as inns along a given road and gradually grow in size, depending on local resources. They can grow larger with the development of a larger road (food being shipped in from elsewhere). They can be upgraded into forts at a cost that is less than building a fort from scratch, and they can also eventually be upgraded to formal cities at possibly a decreased essence investment, if you'd like them to be.
With these kinds of benefits, you could actually choose to develop your road infrastructure in specific strategic ways. For instance, you could decide to create a grand highway from your capital to a distant, newly acquired metropolis in order to assert control over it, while leaving roads that lead to local cities less developed.
Road research could have a whole host of options.
