Any influence mechanics are very very very very very very tough to tweak. Influence plays right now the most important role in game balance. You cannot tweak something that is part of the plan of the majority, especially of experienced players who might run a long term plan. Remember, we are always talking for 3 cards here which are all % based and affect influence: Charity Donation, Propaganda and Conspiracy. They are all uncommon (it is not a coincedence) and as a result influence removalwith voodoo is more stronger than addition. This is also in purpose as the influence system balances the huge gold generation (among with other gold eating features such as officers).
The action of spending gold for influence is what most strong players do. It is an investment. Influence pays back with a lot of ways. Recently, with an extra one; NPC citizens tax which is a huge bonus. Let me reveal how huge (excuse me Barbados); Barbados has MORE than 300M (it's a rough number, not the exact). This is all NPC citizens money. Of course Barbados have spent so far a lot more to get that (ok, they get a lot more things back, not just npc tax income) and this is why(there are of course more reasons) I am entitling influence addition as an investment.
So here we come to the point and the point is how players capitalize on their investment. Right now, influence is a very risky investment due to competition. Voodoo cards helped so far in making influence business profitable in the end. Soon this investment will become less risky, especially for strong nations as these nations will be soon able to use their treasury (there is an IF, if their officials are trustworthy and loyal) on influence (read details
here, it will not be direct). So the players of these nations will now have a bigger margin for capitalization.
Till now, the capitalization margin was mostly thanks to charity donation. Players spent less gold thanks to Charity donation. Now,thanks to nation treasury they will save more gold. However, contest for ports will continue and to some point these cards will define control for the bigger ports (at the very least). To be sincere, I thought that Charity Donation and Conspiracy values would increase instantly only by the news of NPC citizens tax. They have indeed rised but I think that further rize is in the horizon.
Anyway, these are only our views on how game progresses and which are our own estimations. Every player (especially experienced ones) have their own estimations and planning. This planning is what we want to preserve.
So, till a necessity is created this card will remain as it is. We will review this case again in 3 months by player initiative (just create a new suggestion and write up your thoughts). To ease your planning further, no change will ever be made in influence voodoo cards without at least a 2month warning before hand (ie, we will decide any change and then announce the change at LEAST 2 months before hand).