I suppose at the end of the day Cygnus Alpha isn't the most salubrious of places, especially for Vila (nothing to steal) plus Gan is very clearly going with Blake and he is the closest thing to a friend Vila has and, perhaps more importantly from Vila's perspective, a protector.
Well, everyone knows it's not salubrious, but they've been tricked into thinking they'll die if they don't stay and get regular pills from BRIAN BLESSED! So deciding to trust Blake and risk escaping meant being brave enough to risk the possibility of death if Blake was wrong.
But you could be right about the other parts. "Nothing to steal" would certainly be an incentive; I imagine stealing is to Vila like deduction is to Sherlock Holmes, in that in its absence, with nothing to stimulate his mind, he gets depressed and retreats into drugs/alcohol. Also, as Boucher later established, Vila's smarter than he lets on, so maybe he saw through BRIAN BLESSED!'s scam and realized he was better off with Blake.
As for Gan, it's possible they were friends, given that they spent four months together on the London. But it's hard to know, since Gan hardly had any lines in "Space Fall." Though whether they were friends or not, I agree that "I want to stick with the big guy so I can hide behind him" could well have been part of his thought process.
@diankra may correct me here, but I think Vila is the first main cast member to directly kill anyone in the show (you could argue Jenna kills Raiker by moving Liberator but it's an indirect consequence rather than a conscious act).
Also in "Cygnus Alpha," you have that conversation between Jenna and Avon where the latter says he doesn't know if he could kill someone face to face. That conflicts with what we later learned about the Anna backstory, where Avon killed the guy with the exit visas (I can't resist imagining he looked like Peter Lorre). But of course, Avon is cagey about his past, particularly that part of it, so he was probably just misleading Jenna.