I feel like the center of the galaxy could be something special. Be the first one to unlock a certain technology and you unlock the keys to a portal to the center of the universe. Or maybe on the other side you find a ship yard of the Endless Ones. I'm not sure how you could implement something like this fairly, but the idea sounds cool. Maybe there's a 50/50 chance of unlocking a terrible race that launches a massive assault against the galaxy. The the races must come together and put an end to them. Or, if your race is like the Cravers, you become the vessel or allies of this unstoppable force.