if the human race is any indication, I think that other races that may have progressed past our current place probably ruined their planet and all died, because that is the path we are taking now.
Assuming that a few didn't, they next have to get over the travel hump, because we cant travel faster than light, and even if we could safely approach that speed, we are still looking at countless years in transit. Wormhole manipulation would be a technology that would take an extremely long time to develop, and there would still have to be someone at both ends keeping both sides open (Mr. Hawkings came up with that one). This means that they still have to go countless years to keep the other side open, so the chances of that are almost infinitismely small.
Plus, of all places, why would they go here? Because all our signals travel at around the speed of light, no one out there knows we exist because our signals havent reached there yet, assuming they would be detectable at that distance.
Lastly, on a less serious and more Calvin & Hobbes note; if there were intelligent life out there, it would surely be avoiding us.
