Huh, Fan service? That doesn't make sense. I don't recall that a lot of FF7 fans have told SquareEnix to make scenes of Aeris and Zack appearing in the movie. SquareEnix did it because it's part of the story, no way is it for fan service. If it's really for fan service, then SquareEnix would have already told interviewers that the scenes of Aeris and Zack in the movie are not part of the story.
Since Cloud is the only person who can see Aeris and Zack, nobody else can see them.but really is it so far-fetched to think that maybe Cloud was fondly remembering his lost friends? it's common in some anime for the hero/main char. to chase what they think is someone they recognize just to have the apparition dissapear and it's usualy explained as the characters chasing a memory, maybe something simmilar is happening here, Cloud sees his friends then they fade into the ether as they walk away...
So if what you said is true, then it's also not far-fetched for Cloud to see Aeris before her death at the Church (premonition).
There's still no actual proof (unless one of you give proof otherwise) that the Aeris appearance at the Chruch is a glitch. There's a huge doubt on this assumption - FF7 is almost 100% glitch-free, execpt the Aeris one, so please explain why.