Hello again!
I have been abroad for 6 months and I have only had my laptop here so I have not played C:S, but instead Simutrans and OpenTTD. I love the districts in this game and yesterday playing Simutrans I got some ideas for more use of them. Industry chains in these games are much more complex and maybe some of those could be use also in C:S as industrial specifications.
Here are two examples:
Simple industrial chain from OpenTTD with pictures:
http://www.tt-wiki.net/images/ttwiki/f/fa/Cargovectors19.png
In this picture there are 5 vectors: basic, chemical, machinery, wood and agricultural. In basic vector brick, cement and glass works could be one specialization industry making building materials and adding asphalt factory could work too. Benefits of this could be the discount to building prices or maintenance of roads and buildings. Oil could be used for plastic and chemicals in chemical industry specialization. From ore/steel industry could be made cars, ships and train. Benefits of this could be to increase the capacity and speed of public transport, trucks, and shipments. Forestry is making paper and planks and they could be used in some special industry to make books which make schools and libraries more efficient/reduce maintenance and furniture. Then farming industry could be more variated. There could be fishing, fruits, animals. Farming provides raw material to the industry that makes clothes to reduce warming expenses and alcohol to bars to keep tourists and citizens happy and food to the commercial zone.
More complex industrial chain system as an idea for Simutrans:
http://i199.photobucket.com/albums/aa131/AEObikes/simutrans/Goodsv2.png~original
And them some random thoughts:
One district could be natural park which is used of poor tourists(backpackers) and citizens. Monorail and ferry would be great for transportation. Also banks and post could be somehow in the game. Big events and campaings from mayor, like big sport event or rock concert or campaing to increase fertility or to recycle (okay, these are actually policies already).