Multiple Harbors

This would make Island territories a bit better so you can actually use the gains of all that fresh water. In the early days it used to be the case, but the strategy was to only build harbour instead of farms. This needs to be balanced. 

I think having 1 Harbor per Era would be good (may add an additional Technology requirement for each era). This would enable players without the Harbor replacement Emblematic Quarters (Phoenicians, Carthaginians, Norse, Swahili) to stay competitive on sea based maps. This would also enable the Dutch to better exploit their VOC Warehouse Emblematic Quarter without depending on having the previously mentioned Cultures.

Territories would still be limited to 1 Harbor.

One harbor per era, but only one harbor per territory? Are you suggesting, then, to have less harbors? I'm sorry; I just don't understand.

My bad for lack of accuracy. Territories with an Outpost would have 1 Harbor. Cities can build multiple Harbors.