Another way of making the different races distinctive could be to add atmospheres to each planet and exclude certain races from atmospheres. Each race would have a particular atmospheric gas they cannot survive in or one they cannot survive without. In addition they could have a particular temperature range. I'm sure that if this was a desired addition to the game, it wouldnt be hard to balance the availability to planets for each race. For example the terrans might not be able to live in an atmosphere with no oxygen and a temperature below -20 degrees and above 120 degrees. The Torians may not be able to survive with oxygen and with hydrogen but may live in temperatures ranging from -60 to 150 degrees.
Just an idea.