Having spent more than ten years travelling, I can assure you that "there is none as strange as folk."
Aliens even more so.
It would seem provident to look for such a potentially meme/gene altering occurance before it could happen by surprise.
A lotto ticket win might equal that of several lightening strikes, but it doesn't change your chances of being hit again. A very slight chance per cubic light year in a place as big and as old as our universe fast leaves the realm of the impossible and travels quickly to that of the less and less improbable.
Thoughts about SETI and SETI@home
Even if the chances of Alien Cultures are small the effects are so potentially drastic that it would be foolish not to look.
But for the love of good sense no more Viking style maps of our address, as I am not fond of my neighbours let alone beings from outside the heliopause.