The early snatch is definitely worthwhile. I typically go for 40% health / 40% attack / 20% speed for my post-grab units. Having some speed is of value because you may want to add reinforcements to an ongoing assault.
If you want to add reinforcements to an ongoing assault, just retrofit to something that can move again. Otherwise, remain in siegebrick form.
For Econ vehicles, the post-snatch vehicle's value is a product of its strength x speed. So you really want something more like 20% / 40% / 40%. Or even more extreme for boats or planes, which don't need to worry about getting snagged by wildlife.
I have begun to have uncertainty that the strength of an econ vehicle even matters, because I was able to take a city nearly as quickly with scoutwagons. However, the econ strength may improve the actual money earned by a traderoute...but possibly not the buyout time. More experimentation is required to confirm this.
If you can, you want to go all-naval. Naval units are stronger and have longer range than either air or land, and you get the same number of unit slots regardless of type.
Naval is limiting because A: You can't reliably start with them, and B: By the time you get access to them, it may lack relevance to the situation.
The relationship between stats and percentages is not linear. Compare these two military land vehicles:
Name HP% ATK% Speed% HP ATK Speed HP/% ATK/% Speed/%
Spy Hunter 15% 5% 80% 240 12 37 16 2.4 0.46
Pkzw V 53% 29% 18% 467 21 12 8.8 0.7 0.67
Actually, the relationship *IS* linear.
Compare the following: (Military Land)
Speed% | SpeedAbsolute |
0% | 5 |
15% | 11 |
30% | 17 |
45% | 23 |
60% | 29 |
75% | 35 |
90% | 41 |
100% | 45 |
As we can, see, for a vehicle (all vehicles respond the same to speed%), speed of the resulting vehicle is equal to 0.4X + 5, where X = Speed%. This is indeed a linear equation.
Each point of Health (all vehicles also respond the same to Health) is likewise:
Health% | HP |
0% | 150 |
15% | 240 |
30% | 330 |
75% | 600 |
100% | 750 |
From this, we determine that health is 6X + 150, also a linear equation.
Designing a vehicle for 100% power is impossible, as no hull component offers a null adjustment to health/speed, meaning anything you can add will force hull/speed%, so 100% power can only be approached asymptotically. However this table:
Power% | PowerAbs |
0% | 10 |
15% | 16 |
30% | 22 |
60% | 34 |
90% | 46 |
..makes it clear we are dealing with a linear equation again, which appears to be 0.4X + 10. All vehicles respond likewise. Military vehicles inflict Power damage per shot. The relationship is unclear for religious and economic vehicles. Rate of fire is constant regardless of power.
Therefore, here is our results
Vehicle Type | HealthEquation | PowerEquation | SpeedEquation | COST |
LAND | 6X + 150 | 0.4X + 10 | 0.4X + 5 | $1000 |
SEA | 8X + 200 | 0.6X + 15 | 0.4X + 5 | $1500 |
AIR | 6X + 150 | 0.4X + 10 | 0.8X + 10 | $3000 |
As we can see from above, a sea vehicle is, cost-benefitwise, roughly equal or inferior to a land vehicle (We figure that sea vehicles are roughly 2/3 as fast when dealing with initial expansion, as a sea vehicle must traverse the a 180-degree arc of your landmass, while a land vehicle traverses only the diameter) when used for initial expansion, if you start with a coastal city. In addition, for your starting money, you may purchase 3 land vehicles, but only 2 sea vehicles. While sea vehicles have greater range than land vehicles (the exact numbers are unknown) and can outrange city defense turrets, thus enabling them to bombard with impunity, their AI is quite stupid and they tend not to effectively use this ability. Furthermore, two sea vehicles does not constitute an invasion force, and is definitely not worth the price of giving up all the land-based spice wells because sea vehicles cannot capture any of them! Choosing to split your investment is a poor deal as well, as your starting $3000, if split, buys you two vehicles only: A single boat, and a single additional ground unit, with an unspendable $500 left in your pocket.
Air vehicles are, of course, completely cost-inferior in all respects, costing 3x as much as a land vehicle and 2x as much as a sea vehicle, and are unable to capture anything. However, they are faster and able to fight in all terrains, and furthermore, their requirement of 4 cities to even build one necessitates the domination of your starting continent first anyway (It would be foolish to antagonize enemies on an entirely different continent before having finished mopping up yours!). By the time you can build them, you have probably exhausted the utility of land vehicles anyway (there are no transports, so you cannot move land vehicles over the sea, and should therefore disband them all and switch to sea or air vehicles, but then sea vehicles again lose their utility once you take all the enemy's coastal cities), and can easily afford their cost-inefficiencies.
Lots of fancy math I don't have time for can now be used to determine the perfect ratio of health to power in a military vehicle for all combat situations.