I do like the idea of corruption. Although, I would say corruption should be higher at the higher trade volume ports than the lower trade volume ports.
I like the idea of loyalty, in the sense that controlling a port for a long time should give a *slight* edge over those trying to take control.
I like the idea of happiness being something that can be invested in (that has NOTHING to do with influence, perhaps an expansion to building up the port actions)
I think that population growth should be an OUTCOME of port traits. IE: higher happiness, few port control changes (stability) = higher pop growth
I have no idea how the above fit in to resulting in more battles though.