Even if panspermia was discovered to be the answer of how life developed on other other planets, the important thing to consider would be environment. It may be possible that life could emerge and evolve due to panspermia on a planet where the it's atmosphere, gravity, exposure to certain types of radiation, etc, would be lethal to human life.
But that's not the problem I'm referring to. The real dilemma would be in the types of technology those civilizations would develop to communicate with each other. The forms of communication we use are based on our biology; hearing, sight, etc. But what of the lifeforms on other planets?
For example, say that an alien civilization does not rely on sound to communicate, but rather, movement or something similar to a sense of smell. What type of technology would that civilization develop to chat with each other across long distances?
My point is, how would we be able to detect, let alone decipher, something we don't have the foggiest notion even exists? It could be all around us at this very moment, yet we'd never know.