We always play that you CANNOT make any money from selling commodities into your own ports -- you sell to fill the ports, but that's all. It makes for a much, much deeper game. Now a player must decide if he wants the cash or a filled-up port. It also makes the deciding whether or not to take control of a port and when to do it a much more interesting one.

Yes, in the English rules, you can make money from your own ports, and it was either some German version, or some early translation which prohibited this. But either way, if you can simply cruise around your own ports and make cash while also improving your strategic position, it seems that the player interaction would be reduced to "combat or no combat" and nothing else.