Personally, I dislike the navies for the simple fact that they mimic the function of the naval superiority in that other map about European imperialism. Same function for a map of the same theme knocks the uniqueness of this map way down in my mind. The only real difference is that there's two instead of one.
A decay instead of a killer neutral would only be superficially different, as they both still try to penalize players for using the route.
I know that it probably won't help, especially at this stage, but what strikes me about New World, Eastern and this map is that none of them address the reason that the imperialists made the ventures in the first place, which was resources; conquest was just sort of a means to a more efficient gathering and proprietary labelling of those resources- be it slaves, gold, ivory, rubber, or other scarce materials. I read a book called "King Leopold's Ghost" about the Belgian administration of the Congo and it was all about finding rubber, enslaving natives to 'milk' the rubber and making profit off of having exclusive access to said rubber. Ironically, Leopold was seen as a humanitarian for his "efforts" in Africa due to his skillful propaganda- it took decades for any of his admirers to actually visit the place and expose the Belgian Congo as a giant slave factory for producing rubber.
Anyway, the overall balance of the map as it stands seems fine. I just get a strong vibe of the Eastern Hemisphere map right now, and the Navies are the most glaring similarity.
-- Marshal Ney