Some thoughts here.
Any planet that we find in the Goldilocks Zone that has an Oxygen atmosphere will have life, that is to only way that such a planet can develop such an atmosphere.
Now consider the complexity of life as we know it here on Earth. Every breath that we breath contains pollens, spores, microbial life. All composed of thousands of differant proteins.
Now were we to develop a trans-C drive, and found a planet that looked like the Garden of Eden, with a perfect atmosphere, our heroic Intersteller explorer land, steps onto this new planet, draws a deep breath, and goes into instant massive anaphylatic shock. There is absolutely no reason to assume that the proteans on a world with a totally differant evolutionary history would be the same as the ones that we evolved with.
What are the ethics of interfereing with a planet that is developing, or has the possibility of developing, intelligent life?
And what about life not as we know it? Silicon based. Living in an environment that is much hotter or colder, or even under much higher pressure, or no pressure at all.
I cannot remember whether it was Clarke or Asimov that stated that the universe is not stranger than we imagine, it is stranger than we can imagine.
SETI. A wonderful idea, that has already been involved in some discoveries of new things, to us, in the universe. Consider a primitive tribe on a sea surrounded island. Assuming that there are other people somewhere out there, and that they communicate with each other, he faithfully sends up every day one of his subjects with the best hearing, and another with the sharpest sight, to listen for drums and look for smoke signals. Even as the island is bombarded by the electromagnetic signals from geosychronious satellites, as well as other sources.
Moved out to, say, the orbit of Pluto, a much quieter neighborhood, and with a much improved technology, SETI might someday discover a distant civiliazation at about the same stage of development as we are. A civilization with a million years of technological and evolutionary advancement on us? I doubt that we have the faintest idea of how they communicate.