enhanced trade

Well I for one find no foreign trade routes silly...
So I'd like to have
- Foreign Trade routes
- Enhanced trade routes

How it should work
1 - Road connection or revealed sea route (or combination) between two capital cities
2 - In diplomacy, civ A trades resources to civ B
3 - All hexes along the route receive bonuses (Much more gold, little more science). The amount of bonuses depends on the quantities of resources/gold being exchanged. (So, more trade, more bonuses)
4 - A caravan/merchant ship unit appears in a relevent capital city on average every 3 turns.
5 - When a caravan unit is killed, the attacker gets gold, the defender looses gold.
6 - If 3 successive caravans are killed, the trade route is "too dangerous" and the deal is cancelled.

Example
1 - China builds a road to India
2 - China trades silk to India, India pays 6 gold per turn
3 - Hex yields along the route are increased
4 - Caravan unit appears in Beijing.
5 - Caravan unit is killed by Siam. Siam receives 50 gold, China looses 50 gold.
6 - 3 Chinese caravan units are killed in succession. The trade route ceases to function (Yields go back to normal, China stops supplying India, India stops paying China 6 gold per turn).

I like the idea of hex yields increasing along route, but it should be a limited number of yields for a route (e.g. 10 extra gold yields all throughout). Otherwise people would build ridiculously long roads circling unnecessary cities, just to benefit from more yield. It might actually be quite hard to implement that without being exploitable.

You might wanna take a look at the planned mod Fabula Terra, we are sketching a global market feature.