Wardec costs are completely backwards.
Let me explain:
The fiction surrounding 'Concord sanctioned wars' aka war-decs is that capsuleers "bribe" officials, to allow a open state of hostilities between two capsuleer Corps. Now traditionally this has been constructed that you pay X amount to dec the corp, up until now. Now you pay X amount per member of the corp you are deccing.
Well wait, this is stupid; as any person 'on the take' knows, it's not about how many people you are trying to screw over, it's about how many people you have to cover for. I honestly can't imagine wanting a bribe based of the number of people you are engaging vs the number of people you have.
In essence, the solution is so simple. Reverse wardec costs. Force the aggressor corp to pay for its membership to engage the defender corp, not pay for each of the defender corp's members! Retain the ally cost increase currently upcoming, but reverse the wardec cost. Actually Anon brings up a good point below, "Rather than it been a set cost per corp increasing exponentially, make it related to the size of Ally joining the war." This makes far more sense. There would have to be some minimum cap per war, to force 1-2 man grief corps from getting off too easily, I would say at least the current base costs would work.
This way large alliances can still engage small ones, but instead of paying the cost of engaging a small target, they still have to pay the cost of putting their Alliance at war, so large alliances would have to pay for their thousands of members each time they took on a war.
Think of what this does for merc wars, Merc corps are forced to stay lean on membership and effective to maximize their profit. This also fixes the big bullies beating up on the little guys essentially for free, since the "bullies" are now forced to pay for their members to enjoy the right of the wardec.
To prevent any war-dec shenanigans, if a new member joins an aggressor corp during the wardec, the corp is forced to pay for that members entrance into the war, alternatively, disable recruitment functionality to the corp from the first 24 hour notice of a war going active, until the war ends.
Now you have a system where the large rich corps can still dec small fish as the Goons want to, but they pay a steep price. Additionally, similar sized corps will still pay the same price, and once again true 1-2 man griefer corps get off relatively lightly... but that's a better state than the current problems...