I can't remember where I read it but after a certain point in their traval electromagnetic signal become too dispersed to be distinguised from the cosmic background.
Steven Hawking said we should not try to contact advanced lifeforms on the basis of what happened to the American Indian after contact with Europe. The Voyager spacecraft is now sending back data in a different format as if it has been reprogrammed.
In the event of contact I intend to remain xenophobic in the extreme. Reminds me of a story by James Tiptree were man is hemoraging earths resources into space for mere trinkets. 10 buffalo hides for a pen knife.

It depends on whether you believe oil came from decayed life or whether the earth naturaly extrudes hydrocarbons. The equation would greatly be enhanced if we could determine the composition of planets from afar.

NASA freaked and set the spacecraft to only relay its vitals for the time being. Maybe they're afraid of cyber warfar from howeverfar that thing is.