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Reagan apparently once asked Gorbachev if he'd help America if it was attacked by extraterrestrials. Gorbachev agreed, and Reagan told Gorby that he had his back too.

Silly? Perhaps. But it was a popular hypothetical with the 40th president, who often mused that no culture on earth is so different from another that there is no common ground between them. Unfortunately, we as a species are often weak-minded, jealous, hateful, and set in our ways. Reagan often opined that it would take something of a great magnitude, such as intergalactic threat, to unite us as a planet.

The subject was later explored, somewhat more cynically, by sci-fi author Harry Turtledove, whose Worldwar series takes place in an alternate timeline where aliens invade Earth in 1941. The first novel was published in 1994, shortly after Reagan announced that he had been diagnosed in the early stages of Alzheimer's.

Black Zarak wrote:

Oh that wacky Reagan and his alien threats; I was watching a show on History Channel not too long ago about how he'd put references to aliens in pretty much all his speeches, his writers would polish them and cut those bits out before sending them back for approval, then Reagan would send them back once again, largely approved but requesting the alien references be reinserted.

That's not really true. I have a couple of books comprised of Reagan's speeches and personal letters. One of them, "In His Own Hand" contains copies of the physical documents. It was certainly an idea that fascinated Reagan, but it not something he was all that interested in putting speeches. He very much did enjoy posing the question to people though, and hearing their thoughts on the matter. Similarly, there was a joke he used to love to tell everyone about an optimist and pessimist which he also never used in any official speeches. He may have told it at one of the press corp dinners though.

As for not changing speeches, that's not true either. According to former Reagan speechwriter Peter Robinson, Reagan would sent a writer's speech draft with TONS of notes. He would cut stuff, add stuff, and change around phrasing. I have his book lying around somewhere, but damned if I can find it. I believe he had a couple scans of speeches in there too. George H. W. Bush, on the other hand, sent back very few notes on speeches, to the point where his writers sometimes wondered if he even read them.