As I've said in chat making neutral +10% is unlikely to help, as it means two entire plot geographies will want this single type of card, unlike all other splinters where there is some distribution.
The end result will most likely be that neutral cards quickly become too expensive, relatively, undermining the perceived benefit that people currently see. As a result tundra and canyon plots are still disadvantaged, but now it is with prohibitively expensive cards that give the 10% bonus, which means in most cases the status quo persists and no benefit.
I would welcome someone to do the actual math on this, but it's pretty clear the above would be the outcome. I would have excluded option 2 on these grounds, as it's not a solution