But Albow, barracks and other 'military' improvements also represent the industrial and manpower capacity of a city to produce larger and more tech-heavy units-the very types of units which predominate in the late Middle Ages onwards. It has always bothered me that a size 1 city can immediately start building spearmen and swordsmen before they even have a granary or a marketplace!!! I think this is one of those occasions where both realism and gameplay can be satisfied by adding in this feature-with the option for modders to expand as much as they wish! I do think, though, that a barracks should decrease the amount of time a unit requires to become a veteran, but should not automatically create veteran units! Oh, and as for naval units, perhaps you could have a naval acadamy which reduces the amount of time needed for seafaring units to become veteran etc.
Something else I considered was that, for more manpower heavy units, perhaps how many shields a city needs to accumulate in order to build said unit should be based on the population of the city building it. This could reflect the ease with which larger cities can recruit the manpower needed to fill a division of men-at-arms or infantry! Also, it should be possible to build units of varying sizes-either small, medium (default) or large.
Yours,
Aussie_Lurker.