The witches are not my favourite characters. I see these scenes as titillation for an audience wanting an illicit thrill and although the actual apparitions and their messages are interesting, there is little here beyond stock descriptors of evil characters up to no good. Whether it appealed more to James I is another matter. I suggest how Shakespeare may make a direct link to James by use of the mirror in the catalogue of Kings.
A linked post: Some thoughts on Witches and Macbeth