See
this post.
I don't think simple doubling will work. Especially since some things have the same defense. Over all I think some early one should stay the same while middle eras should be increased. For example
Towers (Old)
Frontier Outpost = 5%
Fortified Outpost = 10%
Watch Tower = 10%
Guard Tower = 10%
Tower Keep = 15%
Bombard Tower = 30%
Towers (New)
Frontier Outpost = 5%
Fortified Outpost = 10%
Watch Tower = 15%
Guard Tower = 20%
Tower Keep = 25%
Bombard Tower = 30%
As you can see the "new" outline has a more gradual progression. However we should also consider what other defense structures are in the same era as each other. Such as ...
Walls = 30%
City Gatehouse = 15%
High Walls = 50%
Castle = 50%
Tower Keep = 15%
Mechanical Traps = 10%
Should they be in the same range? or should they be independent of each other? Such as traps not being as effective a a Castle.
Alo should they be adjusted and THEN doubled? Such as ...
Towers (New + Doubled)
Frontier Outpost = 10%
Fortified Outpost = 20%
Watch Tower = 30%
Guard Tower = 40%
Tower Keep = 50%
Bombard Tower = 60%
Thus both doubled and gradual increase.
EDIT: A Proposed Gradual + Doubled values ...
Walls
Palisades = 20%
Earth Walls = 40%
Walls = 60%
High Walls = 80%
Barricades = 100%
Barbed Wire Fence = 120%
Cement Barrier = 140%
Arcology Shielding = 160%
Advanced Shielding = 180%
What do you think? Too much? Not enough?
EDIT2: Proposed Towers ...
Towers
Frontier Outpost = 10%
Fortified Outpost = 20%
Watch Tower = 30%
Guard Tower = 40%
Tower Keep = 50%
Bombard Tower = 60%
Artillery Battery = 80%
Auto-Cannon Battery = 100%
Missile Battery = 120%
Railgun Battery = 140%
Laser Battery = 160%
Anti-Matter Battery = 180%
This one I had to weak a little more. Tried to keep it around the same as the walls. Or have the walls be worth a bit more.
EDIT3: Here is a better timeline ...
----
Prehistoric----
Frontier Outpost (Carpentry) = 10%
Palisades (Carpentry) = 20%
Earth Walls (Megalith Construction) = 40%
----
Ancient Era----
Fortified Outpost (Masonry) = 20%
Walls (Masonry) = 60%
----
Classical Era----
Watch Tower (Mathematics) = 30%
Guard Tower (Siege Warfare) = 40%
High Walls (Siege Warfare) = 80%
----
Medieval Era----
Tower Keep (Engineering) = 50%
----
Renaissance Era----
Bombard Tower (Gunpowder) = 60%
Barricades (Rifling) = 100%
----
Industrial Era----
Barbed Wire Fence (Barbed Wire) = 120%
Artillery Battery (Artillery) = 80%
----
Modern Era----
Auto-Cannon Battery (Manufacturing) = 100%
Cement Barrier (Manufacturing) = 140%
Missile Battery (Advanced Rocketry) = 120%
----
Trans-Human Era---
Railgun Battery (Railgun) = 140%
Laser Battery (Fusion) = 160%
----
Galactic Era---
Arcology Shielding (Shielding) = 160%
Advanced Shielding (Advanced Shielding) = 180%
Anti-Matter Battery (Weaponized Antimatter) = 180%
From what I can see looks like we should have some sort of new walls between Cement Barrier and Arcology Shielding. Mainly in the Trans-Human Era.