Just wanted to throw some ideas here.
Once again, i found stuff in the game files (data_lang_american.txt).
~z~Okay... so we open on an alien life form - vibe TBD - on board a space shuttle
Could this refeer to the alien movie shot at the studios?
~z~Your lunar and solar spheres are out of line.
I believe this one is Lester. Eclipse anyone?
~z~Now once you're in there and you've got the score,
~z~Beam up to the mothership!
No idea, but, hey, "beam me up"... And "the score", any reference to the mural found about karma stuff?
Plus, the mothership could be The Truth's truck (http://gta.wikia.com/The_Truth)
And the guy gave you some insights about the JetPack in SA. Did anyone spotted him in GTA V?
In the core of the mountain, where the blast is not felt, there you shall find it.
Again, points to an underground hidden in one of the mountains.
Here are some more:
~z~"See, the ships are coming, but these walls will hold us..."
~z~Let's Beam Him Up
~z~The last dinosaur in town is about to get fossilized.
~z~Zondar! That aircraft has been blessed by Kraff himself!
~z~Come in, light aircraft. Identify yourself and state your intent.
Are you able to look at things and see them as metaphors for other things, like trees and eagles?
Regarding the tractor being abducted by an UFO, for now it seems that NOBODY actually tried.
EDIT: also found this CD from epsilon: https://play.spotify...WcJ1NK60DGBJMn0
it can be bought on itunes as well. Probably irrelevant, but i can't listen to it.