Life must have evolved on other planets and yes there must be other Earth type planets. The Universe if not The Galaxy is too vast for this not to have occurred.
However I think, on a cosmological scale, the life of a planetary bound technological civilisation might be too short for two such civilisations to evolve at the same time in the relatively small sphere that we can monitor.
As for a technological civilisation that is not planetary bound...........
Well to visit they would have had to solve the seemingly insurmountable conundrum of space and time called superluminal transit. This would indicate an extremely high level of development so why would they ponce about buzzing fighter planes, spooking airline pilots and the rest of the nonsense accredited to UFO's. I suggest they would announce there presense openly, laugh at our non-existant means of planetary defence and proceed to take over the Planet and exploit us. Simples.
