i thought ships had a fusion drive that required no supply. - anyway.. when its about the engine effects. i think they are of course only for the looks and to underline certain characteristics rather than economical issues concerning the factions.
liberty with their rings look light, clean, and sort of pure - with mainly silver, white, blue colours
kusari are traditional, like their ships - a fireanimation and fire colour
rheinland is just underlining the heavyness. their ships look like factories with wings and so they need exhausts that are smoking something that looks poisenous.
trying to interprete too much into it wont work, i think... unless igiss makes something up for it.
when it comes to economics - i do not think that chris roberts payed any thought on "if the economy would really work and if every faction gets all the supplies they need" - but yes, its fun to speculate about it....