Managing the economy, expanding as fast as possible but not overspending, is an important part of the game.
I don't remember this exactly, and I don't know if some of those civilians could be alive, although in that case I think they would count as saved. But I think civilians give you positive points only if not killed (saved), but they give you negative points only if killed by you. That is, you get no points, positive or negative, if they are killed by the aliens (not saved). I'm not sure about this right now, though.