Why make Reagan's mom a movie star? What did that add to the plot?
Yes, I am aware that W.P. Blatty based the characters on Shirley MacLaine and her daughter, but what did the movie star angle bring to the story?
Yes, she had a circle of illustrious friends, but that could have been accomplished in a more suitable way for the Washington setting by having her be a politician. Anyway, all the parties and guests didn't add much beyond the scenes where Reagan acts unacceptably in front of the guests.
We didn't see anything specific to a movie star in the film other than the one film set scene. No gossip columnists pursuing the story of the strange things happening to the daughter of this big star, nothing. The drunk director could have been a senator or some other politico to match the DC setting.
For all they did with it, I don't see any reason for Reagan's mom to have been a public celebrity at all. She could have been just some regular single mom and perhaps her situation would have been even more relatable for the audience.
While I am on this topic, do you think that having the death of Burke Jennings (the drunk director) occur offscreen was a mistake? I admit I did not associate the head-twisting scene with his murder until fairly recently. I had just thought of it as Pazuzu wanting to do something hideous and shocking.