I think that there is not a good way to level a Conster "peacefully" at the moment.
Today it means to have a droner (that everybody recommends for obvious reasons), or another fighting char, and lom it to a conster later. But I think this is not the way traders want to level. If a player does not want to fight this should be also a possible play style.
In my opinion building stuff and doing missions should provide enough XP to level a conster to near cap, at least for his main skills INT and DEX.
All it would need would be more XP for building stuff and for the HQ missions.
I think the Researcher can be leveled quite good with the missions and ressing stuff, but if I am wrong they should get a second look too.