I don't think missions should be anywhere near as profitable as trading. Completing missions over and over again does not provide other players with many roleplay opportunities: you go on average 30k away from a base, kill npcs for a few minutes or longer (depending on mission difficulty) then return to base. You are close to a friendly base, so you're "protected" somewhat. You don't have to venture out into new systems with potential hostile players in them - like traders have to.
If missions were more involved, for instance an Outcast mission to destroy a Corsair base in Omicron Gamma, then maybe they should earn more. As the outcast would not only have to travel out there (potentially meeting more players to interact with), but he'd have to interact with the inhabitants of Omicron Gamma.