IMO, separating naval & land access is clearly the way to go. There is a big difference between having ships in your ports, & troops on your territory. I think this is a feature that could be developed much further than it is; there are many possibilities.
Have the ability to restrict land access to certain places, & for transit only. No more armies stationed on your land.
Restrict the size of both fleets & armies which may use this, at any given time.
Restrict it further for countries at war. You might flat forbid military access for combatants, period. Or for those at war with certain favored countries.
Have access granted, generally, but need specific permission in each case it is used.
There are many permutations possible. This is a good example of where modding ability would help test for the best options.
As far as the maps are concerned, I'm not so sure. Without the ability to trade, we'd have non-exploring nations unhistorically limited to a 1453 knowledge of the world. By 1653, all of Europe knew where Virginia was. OTOH, the current system does, undeniably, allow unrealistic exploiting of this (Venetian or Pomeranian colonies in Madagascar), so some limits are in order. I think the policy traditions may go this way, but don't understand them well enough to say more.
