In his excellent book The Art of Pastoring, David Hansen offers an interesting insight into the benefit of theological reading:
Good hard theological reading makes my sermon preparation go faster. I've noticed this for years: two hours spent reading an author like Barth, Forsyth, Edwards or Bonhoeffer on Wednesday saves me hours of sermon preparation on Friday and will produce a deeper, more searching thesis. Such writers teach me to think Christocentrically. Thinking Christocentrically helps me sort through the side issues and leads me straight to the heart of every biblical text and the subject of all sermons: Jesus Christ.The more searching my understanding of Christ, the better my sermon preparation. Given my antipathy to time management schemes, it's a little hard to admit, but reading difficult theology is one of the best timesavers I know.