I just tried to look up the differences in quality for spaceship weapons, but didn`t find any, only an example how to aquisition. Can anybody help me out? do the rules for personal weaponry apply or what?

There are currently no rules for starship component craftsmanship. It is up to the GM as to what effect they have.

I would make "Good" quality macrocannons/lances add 1 to their max range, and best-quality add +1 to their damage, personally. Alternately on Lances I would increase STR by 1 for best quality.