Alien has been fueling video game and japanese monster design for thirty years.
Blade Runner begat Blind Justice. and Wipeout.
Not really a tie.
While "Alien" may of had a bigger influence, I think Blade Runner made alot of people think differently about the future and how it can be thought of. Fifth Element, for example. Blade Runner had more of an influence to science-fiction/film, than those examples you mentioned.
Anyway, no need to debate over Alien and BR. They are both great science-fiction films. Both made by the brilliant, Ridley. Why fight?
As for "VS" films...Godzilla seemed to do well with "VS" films and there's going to be a remake of Friday the 13th, so the Freddy and Jason movies can still be made seperately.