With that in mind, I make the following suggestion:
Make influence in ports reflective not just of coin spent and/or voodoo cast but have ships and more important ship gun power serve as a multiplier of said influence. Its how things worked in the historical period and it fits more the advertised genre of the game. Two players spend coin or cast on a port to affect influence, each should have the total gun power of his or her combined fleets factor as a multiplier of said influence.
Edits:
Initial ideas:
The suggestions made by Alkie and Synaster are exactly what I'm looking at and I would prefer this be a collaborative effort as I don't have the years in some folks do in this game.
I'm not sure if the idea of ships (ie: synaster's)
0-50 ships = 80% influence multiplier
50-100 ships = 90%
100-200 = 100% Influence (all of it counts)
200-250 = 105% Influence
or Alkie's
x.05 gun/fleet power (Governor)
etc
x.033 gun/fleet power (Captain)
x.03 gun/fleet power (Pirate or Citizen)
is a better basis?
ideas, thoughts etc