I like the Idea of thoskins, but I would add a nessesity of some modifications by the engineers.
The engineers are far to unimportant in the current versions, because everything they can build is either quite expensive or only needed in very limited quantity... if the aircrafts were cheaper (or free), but would need a great part of engineer time there could be a decision like "do I need more manufactoring capacity or will I invest in more hangars, another base, etc"
Raw material and normal human technology could really be provided by the council members, while advanced technology has to be captured.
ps: I thing a great problem of the discussion is that there isn't enough differentiation between game mechanics and storyexplanations...I think the game mechanic works quite well....but it feels quite wrong if the aliens arent enabled to destroy your aircrafts