[Suicide Junkie]

Rather than calling them "Captains", and saying that a ship can be without a captain, the components should probably be given a different name.
"Legendary Individual" perhaps, or "Elite Crewperson", depending on how special they are.

You could then include chief engineers (+1 repair, maintenance redux), first officers (smaller Version of captain bonus), and others.

You mentioned that the captains would cost minimal resources... Especially for the frighter captains, the component would be almost a requirement. A freighter captain could easily pay for himself many times over, which is good, but it should be an investment decision with a year or two before you make your money back.