Good question, and of course only calibrated speculation can propose some answers.
In the first place, it's obvious to any objective observer that UFOs are
not new-comers in our skies -- or better 'heavens', because that's what our ancestors used to call them. It bares no doubt that this must have had a tremendous influence on a human non-technological and gullible mind-set that characterized ancient eras.
Just as there are UFO cults now, there was a highly religious reaction to the -- as that etymological root for 'God' indicates -- 'powerful beings from heaven'. Notice the plural. UFOs have interfered in our spiritual translation of the cosmos towards religion, and undeliberately caused a shift from our original mythological pan- and multitheist religions towards the viewpoints shared by the three pillars of monotheism: that everything sacred is in the heavens, and that these are occupied by superlative beings to who in comparison we are but poor sinners.
I don't know if that's a good thing, considering the tremendously fatal divisions these shifts have created amongst earthlings. I can even suspect that these beings have interfered genetically in our biological history, to 'straighten out some things'. If that were the case, I also would take that to be a dangerous idea.
I also have come to the conclusion that so-called grey variation of extraterrestrial beings -- humanoids really -- has a quite prophetical motivation, warning and giving incentive to hundreds of direct experiencers about an impending ecological devastation. That pattern is proper to every single direct contact there has been that we call 'abduction'.
But ontologically, the existence of extraterrestrial intelligent life will quite vastly expand our consciousness. Over time, our planet would undoubtedly come closer together internationally, at least in absence of racist agendas, which unfortunately is not the case. Our 'world' would extend away from the abstract chaotic idea that we now have of it, and finally revalidate the cosmological order which we share with the other planets out there, as was appreciated before by so many natural philosophies, both East and West. And that can only do us materialistic fools some good, I would think.