[dogscoff]

Trading for a race that breathes the same atmosphere accomplishes nothing except make your people angry

Not true. Put 2 million Terrans on a planet. in 10 turns you'll have 3 million population.

Now remove the population and put 1 million Terrans and 1 million Cue Capp on the same planet. In 10 turns time you'll have 4 million population. Doesn't seem like a big deal but in Proportions games, for example...