One thing that strikes me about claims of alien visitation is that so much of the evidence is musty and fusty.
Every day, I get stories and articles from people around the world who aggregate UFO news. But much of it is not news -- it's olds. The folks who think there's good proof that Earth is a stomping ground for extraterrestrials are still hung up on the Roswell incident of 1947 or its British opposite number, the Rendlesham Forest event of 1980. They're still citing the testimony of aging politicians, defense establishment types and Apollo astronauts who "know something."
The few alternatives to this vintage archive are contemporary photos and videos of vague lights in the sky, low-resolution and low-confidence material that isn't likely to sway many scientists. The good stuff seems to be the old stuff.