Here are mine.
1) No PP upkeep cost for any naval units in port. In other words, if your battleship (or other units) stays in port it doesn't cost anything.
2) Reduce PP upkeep cost for submarines at sea to 1PP.
For #1: I think it is a way to prevent players from disbanding their battle fleets because of the 4 PP per turn cost. You only pay for upkeep when you actually use your naval units.
For #2: The two PP upkeep cost for subs is steep given what they accomplish. For example, in my last CP game with priviliged AI my starting U-Boat managed to sink 11 convoy points and 2 points of the Canadian Corps in transit. I calculate that as a cost for the Entente of about 114 PP. But my upkeep cost for that U-Boat before I disbanded it on turn 90 was 180. And I suffered 5 points of damage. I calculate this as a net loss to me of about 194 PP. If I had been more successful at locating convoys, I could have broken even, but only at the expense of triggering American entry.
I know the Units file can be edited to change the upkeep costs, but I don't know if there is a way to mod the game without getting into the exe. file to kill upkeep costs for units in port.