Guest posters are a good idea for all blogs. Different people have different ideas, different writing styles, and different ways to connect to visitors.
Not only is it a good idea for your readers, it’s a good idea for your blog.
The more authors a blog has, the more content that will get generated, the more active the blog will appear and, when that happens, search engines can give more rankings and traffic. All of this leading to more sales, revenue, or whatever the blogs KPI is.
More bloggers help out a blog in more ways than one and growing a blog with multiple authors, or guest posters, is a win-win situation.