On the note of mechanics, my brother (who's a mechanic) offered this insight (which I had to have him write down, I'm no good with cars myself. x.x):
You get a brand-new older car you want to make faster. So start with basics...first headers and dual exhaust (G1). Then (on older cars) remove the belt-driven fan and replace it with an electric one (G2). Then polish the insides of the intake manifold for smoother airflow (G3)...each step adds more power, at cost of fuel efficiency and some extra wear, of course.
Then you get a different car. You want it to be fast too. Which means...doing the same steps on THIS engine, because what you did on the old first has no bearing.
Each grade on a module is a step in the process of adding all the modifications, one at a time, and each roll within the grade a "tuning" stage to maximize the performance of that particular modification or add-on.
Works the same way with lightweight modifications. First you remove unnecessary bits. Then replace a heavy piece with a lightweight replacement. Then replace a heavy steel frame-bit with an aluminum one (G3)...and so on and so forth.
Brilliant!