The daily lost of influence drops by 0.02% each level.

At level 20, 0.4% drop of 1 %, which means that you lose 0.6% influence daily instead of the usual 1%.

1000000gc first level, increase of gc cost of 10% each level up.
Cost 100 gold bar each level.

seems way to weak, and way to expensive.

as it is we lose 1% of the influence if its above 5K.
so lets say 10M in one port= 100K loss.
at level 20 of this tech reducing 100K by .4% it would be reduced by 40 gold. unless you mean the 1% would be effected. so it would change from 1% to .6% at level 20.
in which case the loss would be 60K. which would be a pretty decent discount. so if its the second I give it a +1.

I know it's kind of confusing but it's the second, at level 20, u lose 0.6% influence daily instead of the usual 1%.

I see. you may want to make it a bit clearer in the original post. i suggest you simply state that at level 20, instead of losing 1% a day you lose .6%.
but i give it a +1. would make influence so much easier to maintain.

Influence is pretty easy to maintain I haven't kept my influence up but when it was at its peak 2.5m it wasint much and I was running off opm

it is easy to maintain generally. but I'm all for making it easier. combine this with political science and you could maintain 10M influence with around 50K. maybe less.

this would enable merchants(and any pirates who want high influence aswell.) to reduce the amount of gold needed to keep up their influence, saving them gold and making them slightly richer, which in turn makes them more profitable to raid.

Not sure about this, there's already a tech that increase the amount of influence you get from building the port up. I don't know if you should be able to increase your gold-influence ratio and decrease the decay

Slowing decay is not as bad as stopping it completely, to me, I think maybe the cost can go up, but at level 20, the cost would be very big already. So, this is fair.

Slowing decay will be very neat for the big influence players. More important than the extra influence increase technology, I believe. I think this is a good idea - but it must of course be priced correctly.