I'll volunteer the title of a great book: The Analogical Imagination, by David Tracy. In it, he examines the way classics, literary and otherwise, provoke us to deeper understandings of people with different religious beliefs. Along the way, he takes a very broad look at Christian traditions and the practice of theology. It is a book about how to think about theology. It's challenging reading, but very rewarding.
One of the things Tracy writes about is to consider your audience. Theology that you write for academic purposes has academic standards (rigor, logic, a consideration of prior work, perhaps complexity, perhaps originality). Theology that you write for apologetic/polemical purposes has far different standards. And what Tracy calls systematic theology is different still.
Systematic theology is a reinterpretation, a re-vision of the Christian story. As such, it could be fiction, or art, or exposition like Mere Christianity. Systematic theology doesn't justify itself through argument. Instead, it attempts to inspire recognition, and empathy. Every unique person has their own story to tell, and every culture needs to hear it in a personal way.
Some recent Christian writers whose work you might consider are Philip Yancey and Donald Miller. As far as I know, they're not doctors or magicians. They manage to write poignantly, personally, and honestly anyway, sometimes about Biblical things, and sometimes just about life. It's theology, but it's not really academic.
ECPA is a consortium of evangelical publishers. You might go through their membership list and see what kinds of nonfiction they accept. Zondervan is only accepting academic titles, bible study aids, and ministry resources. Tyndale wants no academic work, but popular practical applications.
One of Tyndale's pages recommends establishing yourself with a portfolio of credits in Christian magazines. This helps them (and an agent) take your book proposal seriously. Maybe that is another path to nonfiction writing apart from the PhD.