Maybe the aliens will give us the cures to the diseases?
What have we got to learn from SETI? That we are alone in the universe? And what if we aren't? What then? That aliens think we're a bunch of retards and don't want anything to do with us?
Quoted from http://genomeathome.stanford.edu/science.html#real :
Increased medical understanding of the human body and it's inner workings will inevitably lead to better medicines and treatment of diseases. In other words, Genome@Home saves lives!