We've found signs of very primitive (microbial) life activity on other bodies within our SOLAR SYSTEM. I think it's just as likely that sentient life exists within our galaxy besides us as it's likely that a block of cheese will get moldy if left in the fridge for a few months.
Also, Earth may be a tiny speck in the universe, but so is our galaxy. So is the entire observable universe. To say that we are insignificant seems ignorant to me. Every living being, from the smallest microbe to the greatest leaders and innovators of our society experiences unique circumstances and contributes those experiences to the collective. I think the goal of humanity shouldn't be to physically reach other sentient life, but to share the collective uniqueness of earth with others in this galaxy who might be wondering if they are alone. My belief is that we should be shooting signals out into space containing easily decoded encryptions of dictionaries, encyclopedias, history books, textbooks...in the great scheme of things our knowledge is our greatest asset we have to share. We should reach out to any other possibility of sentient life, from apes to aliens, and try to share that. Chances are that most other life that we encounter will be much simpler than us (it took hundreds of millions of years for humans to evolve into sentient beings, and tens of thousands of years for us to develop technology that makes space a reachable horizon) or vastly more advanced than us. I theorize that we would gain a lot of insight from observing less evolved life on other planets, but it would be a mistake to try to inhabit those planets ourselves. Look at what happened when Europeans colonized the Americas. The Europeans brought over disease, greed, and government and succeeded in eliminating much of the rich indigenous culture that we now have very little left of to study and learn from. Likewise, I think that a more advanced, enlightened culture that finds us would be likely to understand that, while we are less advanced, and truly barbaric still in many ways, they would stand to gain more from learning from us than abolishing us. I believe that the reason we've been unsuccessful in finding signs of extraterrestrial sentience is largely because our society is too focused on war, conquest, and imperialization. I would not be surprised to find out we are being studied by more advanced alien life, but my guess would be that they're uninterested in revealing themselves to such a warlike and aggressive society.
