I think it might be interesting if, when you lack a module you want (Or, in some cases, -need-) to use for your airships, you could try to research it, rather than waste time trying to guess which cities you don't currently control might have it, or wasting time AND money on spies.
Not necessarily replace, mind you, but having an alternate method would be nice.
Also, it seems a little silly that you need to -keep- those cities if you want to keep building the modules. It's not as if people are just going to forget how to make fire extinguishers or telescopes, and considering that the same ship design can be built in many cities at once, often on opposite sides of your empire, I doubt they've neglected to build heavy cannon factories in multiple cities.
Air Lord, Engineering Corps
I think cities need to have specializations to make the campaign run more smoothly and not try to circumvent this. A city that makes steel as their main export is not all of a sudden going to turn into sugar bunting over a month and start to make bread, mind you!
I't would make sense if this process took a lot of time/effort and if the finished product was not as good as the cities that make it for a living (either time wise or price wise).
Its not a bad idea but there needs to be some incentive to be more aggressive in the campaign and not turtle until you have unlocked your valiant death machine of campaign-winning awesomeness!
fire bird you are on to something but maybe the academy could unlock simple things like the telescope or fire extinguishers so that you can get these things quickly and not scavenge around the map looking for the city with telescopes.