I don't think this has to do with the "optimism" of the 90's, just that it was a time when conspiracies were not so heated.
But Knight, this is a GREAT topic for you since much of your interest in space has been cultivated by pop culture. Though this is mostly me getting this useless info off of my chest, because I'm likely not going to be doing a TED talk any time soon.
WARNING: LONG POST!
I'm interested in this particular piece of 90's fandom, not so much because of aliens alone, but because of how an interest and belief in something can become so perfectly brewed. And from there, how much about UFO sightings/experiences are very much the byproduct of pop culture.
The 90's alien craze was a mix of LOTS and lots of pop culture and some "real" UFO incidents and/or related major news stories, and basically you have a cycle of people gaining interest in UFO's from avenue then feeding further interest from the other avenue.
Worth noting that in the late 80's some books were released about the JFK assassination and the Roswell UFO debacle, which plant some seeds for what's to come....
Oliver Stone released JFK in the early 90's, using one of those books as a direct source. Then HBO (in 1994) piggybacks onto JFK with a movie of their own, Roswell. Both of these movies spark an interest in these conspiracies. Not to mention in '92, The X-Files was released.
THE INTERNET: About '94 lots of people are now going online- and the two most popular searches? Porn and UFOs.
Alien/UFO merchandise starts piling up- and grey aliens and flying saucers are public domain, so no licensing is involved!
Talk about Area 51 was already making the rounds but now is really popular. Originally the public could purchase photos of the site at UFO conventions, supposedly from Russian sources. Now they're on the internet and the subject of TV documentaries and movies. Speaking of...
Many networks begin milking the UFO interest with documentaries, made for TV movies, and even more TV shows (like Dark Skies, for one).
As for documentaries, the biggest one being FOX's Alien Autopsy. (This film was proved to be fake later on, even people involved came forward to admit this... yet we still have people who believe it and claim that those autopsy producers are just saying it's fake because "the government told them to".)
Art Bell's radio show rapidly grows in popularity. Again, with the internet more widespread, Art Bell's website is a big reason for this rise.
In the news, there's various reports of "real" UFO stuff: things like the Phoenix lights, the anniversary of Roswell (and the Air Force issuing a public explanation about Roswell), Bill Clinton being asked about the existence of ET, reports of water on Mars possibly having life, the Chupacabra becomes a popular new crypto-critter, and much more).
1996- Independence Day is a huge hit ( thanks to massive media campaign, and it's the first big budget film to have a web site). ID4 references so much about UFO culture- Area 51, Roswell, abduction, even The X-Files. Fun movie, despite so much dumb stuff in it.
Other films: Contact, The Arrival, Men in Black, The X-Files movie, Fire in the Sky (Travis Walton abduction story), and much more.
Studio execs could easily sell a UFO movie in the 90's because you had other UFO movies and TV news reports as free PR.
Then interest waned before the 90's ended. It picked up again decades later after 9-11 rekindled the conspiracy craze...however, even with cameras now being so abundant, we have less UFO photography. There are plenty of obvious fakes though.
I'm probably missing some things but there's so much involved here. There are even records which reveal the rabid frequency of how often these topics popped up in internet searches and print articles throughout the '90's.
