The downside is not only is our planet, the stage onto which humans wandered a mere 200,000 years ago, a youthful 4.6 billion years old, but the universe itself at 14 billion years old is barely out of nappies. What this means in practical terms is that we've arrived way to early at the party to encounter any advanced alien civilizations. We'll be reduced to cosmic dust long before we get the chance to meet any aliens flying round in spaceships.
On one level that's incredibly depressing, on another its gives us a unique advantage over any other civilization that comes along in the next 100 trillion years or so. Only humans have been born close enough to the Big Bang to look back in time and understand the origins of the universe. Given the rate at which the universe is expanding the civilizations that follow us will be largely clueless as to the origins and evolution of the universe and perhaps their place in it.
It's pretty awesome, unless you're a creationist, to think that we possess scientific knowledge that no other species will ever have for as long as our universe exists. But it also places an incredible responsibility on us, after all we surely have a duty to preserve that knowledge and make it available to others? Our legacy to the universe. Which would of course make a cracking premise for a sci-fi story.