Haven't read every word posted here, but am I the only one to posit that, if the Reavers themselves are too aggressive to maintain their own ships, might they use that same aggression to subjugate captives from the ships they raid and force them to maintain the ships? We haven't seen the inner workings of a Reaver ship, have we? Maybe they don't kill, eat and rape (order interchangeable) all of their victims - at least not at first. They could be like the Pakleds ("We look for things - things to make our ships go, and then we eat and rape them").
It all boils down to whether you can buy that an atmospheric gas made Reavers psychopathic towards normal humans, but not each other. I don't buy it, for reasons stated above, and I for one have said my peace on the matter.