But in all seriousness, Occam's Razor is a great tool here. So far, every cosmological problem we believe we've figured out has occurred due to natural processes. There is very likely something we don't know about large scale structures (an understatement!).
* All intelligent life goes extinct before achieving interstellar colonization, or is content to remain in their home stellar system.
* We are in the first generation of life in the galaxy capable of achieving interstellar colonization, due to the time scales required for sufficient heavy elements and evolutionary complexity to arrive.
I've always viewed the Golden Record as a way to make humanity feel better about its future. The need to leave a legacy behind is core to who we are, and that's exactly what we did with those two discs. We left something behind that will survive for 1 billion years, with the infinitesimally small hopes that someone will find it. But, it makes us feel good.
Besides, even if this was the works of some super duper advanced civilization what difference does it make? Our quest is to explore and learn new things, whether they were made by nature, God, or any freaking alien out there is irrelevant.