I very much admire Lewis' evangelization, and share your wish that I had learned more of him in college. I have 14-15 of his books, and just dusted off Miracles in the hopes you might still want to discuss it, or some of his others.
One of my primary reflections generated by Miracles is whether Lewis chose a very narrow definition for the term miracle (p5)--I look for the hand of God in everything, and pray frequently for His Intervention in all kinds of mundane things.
Don't be put off by Lewis taking his own sweet time getting to much discussion of specific miracles--he does in fact get there by Ch 14, even though at pg three I thought he might be saying he wouldn't go there.
I think Lewis can be hard reading because he thinks so much more deeply about things than I do--I'm afraid I've been programmed to look for the quick sound-bite answer. I've learned to bounce to the next chapter, or back to review the last when Lewis gets over my head, and come back later to the hard part--I've really enjoyed his books, especially Mere Christianity, Surprised by Joy, Letters to Malcom, Pilgrim's Regess, Great Divorce, Weight of Glory. I hope you do too.