In the online RPG discussion space, Mothership is certainly brought up more than Alien, but I think this is less about Alien's audience being collectors, and rather that the Alien IP works against the game as much as for it. From what I've seen, there's a false perception that in Alien, you're going to be dealing with Xenomorphs, and only Xenomorphs. The idea that the game can involve other entities as antagonists doesn't seem to occur, even though the Alien franchise is riddled with them. Mothership being billed as general sci-fi horror means people assume it can do Alien, The Thing, Annihilation, etc., while Alien can only do Alien, even though Alien is the better designed game.