SPORE Grox Homeworld???
I think I've found the homeworld of the Grox. It is the nearest star system to the Galactic Core, which is in the centre of the Spore Galaxy (obviously haha). As far as I can tell, it is the only one of their planets to have more than two cities (I could be wrong here, but I've visited a lot of them!) Also, all the lines of the Grox Empire seem to run from this system in the galaxy view.