[Suicide Junkie]

Should a modded component cost more than the Fractional reduction in space?
IE if the 20kt Version cost 200 mineral, should the 10kt Version cost 100 or 125?

IMO, the smaller component should cost slightly more (125), but should certainly be less efficient.
IE: 20kt cargo that gives 750 storage VS 10kt cargo that gives 300 storage.

Should a "Swiss Army Knife" component cost more than the sum of its parts?
IE: 20kt ECM + Combat Sensors + Aux Bridge cost more than the sum of each of them separately?

Definitely. It has the added value of saving 10kt of space, and reduced repair time.