How does Armour and Wrecking Kits work?

Yeah, upgrades are actually multipliers.
For example, Spectran's wrecking power / "crash-damage multiplier" is 2.0 .Apply heavy wrecking kit (crashpower=2.15) and you'll have 4.3 wrecking power.
As for armours, you'll need to take a look at  "# own crash armour" or "# Energy loss at 1000 kg*m/s Impulse".For spectran, this value is 0,016.Install heavy armour kit (energyloss=0.45) and you'll have a value of 0,0072.The less, the better.
Deform factor is basically the build quality of a vehicle.Your vehicle won't be affected much from impacts if this value is low.Spectran has a value of 0,8 whereas for Wrecker, it is 0,45.Again, the less, the better.

Hey @outblast
Is it just me or Wrecking kits don't add missile capacity
No matter which Wrecking Kit I apply the cars always have 15 missiles.