I think a lot of these questions depend on 2 things, 1 the back-story for all this (including the years between GC1 and GC2) and the alignment of the races (i.e. pure good, chaotic evil, balanced neutral etc..).
For example if during the period between GC1 and GC2 the humans have managed to send out many more probes and find out where all the "good" planets are then maybe they will also already know where the best ones are... Or possibly the opposite has happened and the war has destroyed a lot of the other species data on planets and so they've lost out, maybe it's data that can be traded...
Also with regards to how the other races act (what tech path they take, what ships they design, etc.), taking into account something that "King in Yellow" said in earlier, would it be something along the lines of the Yor (being "machines") are more likely to go for lasers as precision weapons, where as the drengin would have mass drivers (big hard hitting, but less accuracy) and the Alterians would concentrate on their defences, maybe balancing shields and armor. The general tech tree would again depend on the story and alignment with there being vague good, evil and neutral paths which would then depend on whether that race is more warlike, money grabing, diplomatic etc.
Also within diplomacy another thing could be that if you're playing the Drengin and you need to talk to the Torians there would automatically be a high diplomacy penalty, the same if you're the Drath talking with the Alterians and visa versa.
Anyway back-story and alignment, all good...