On what grounds can one argue that theology is more than an intellectual exercise?
To denigrate theology as an "intellectual exercise": is a hallmark of a movement known as the "new atheism" which disapproves not only of religion but of much humanistic thought as well. Its practitioners are often philosophically naive. There are several grounds on which you can argue against this.
First, whether some divine being does or does not exist and what effect that may have on our lives is of immense importance, and our answer will affect how we decide to live in many ways. Even atheists, in deciding that no gods exists, must think theologically to arrive at that conclusion.
Next, theology has a long tradition of wrestling with ultimate questions, especially moral ones, and reflection about such questions is again important for how we consider our place in the world.
Finally, even if we are not concerned about religion in our own lives, unless we understand other people's theological commitments we will not be able to function well in a multicultural world, where Islam, Christianity, Judaism, and Hinduism, for example, are all very important.