Some nice points coming through but I think you are being a bit slack with the referencing.
If someone else wants to investigate the merit of your claims you ought to specify the time code within the films being referenced.
Did you manage to track down any texts of a psychological nature which might provide theories for how the 'boo effect' might work and how it might be applied? or is this purely down to your observations? if so, what other story telling devices are being employed to deliver the punch? how is the scene set?
The film could start with showing the zombies rising, it could also start in many other ways. what is the justification for needing to see the zombies before the reveal? is it obvious that the band are playing to zombie before the reveal after the power goes out? if not, does that matter? isnt the purpose of of the reveal to present the audience with a surprise, given the context of this film being a music video, are audience expectations only that the band will perform the song on stage?
Could your altenative be delivered in the proposed 20 seconds? can you list examples of where this has been done? it doesnt have to be the same genre?
in return of the living dead they go to great length to explain where the zombies came from. i agree that it is not explained in the trilogy you are looking at, but why is this important? considering the films explaining the zombie origins is a minority(which you havnt evidenced) does this explanation prevent the film from working? what is it about other zombie films which allows the story to work despite this lack of explanation?
Can you provide examples of other 80s splatter horror which you are drawing your comparisons?
You mention evil dead, but what specifically is it that your are refering to as a similarity?
You state that all the band are equally infected in film 2, but is that true?
again, more general referencing to 'films of the period' but no mention of specifics or why they are relevent. might be nice to see what films you are referencing for this conclusion.
With film three you mention the obligatory sexploitation but was this something associated with modern day zombie films? was this used in earlier films? which films support this claim, but importantly, which films challenge this claim?
do zombie films have to end on a bad note? why? any examples?
return of the living dead is cyclic. but how does night of the dead end? dawn? day? planet terror?
but it might be cool to investigate some films on the fringe of what might be considered zombie. what is it that at the core of zombie film genre?
do films about virus count? if not why? what about end of days type films? what about invasion of the body snatchers?
at what point does a zombie film stop being a zombie film and become something else?