Do writers accept suggestions on plots for books? Would you receive credit?

I guess it depends on the person. I teach literature, and some of my friends are writers. Some of them have asked me (and some others) to read their drafts, or share their ideas in order to get a general opinion. Some others simply like to work alone. If I was you, I would ask mostly: a. people who read this kind of literature; b. people who you really trust. Ultimately, I guess, the decision on what to do with the plot will be yours, regardless the feedback you get.