Rereading His Dark Materials is definitely worth it. I did that after I read La Belle Sauvage because I realized I remember so little of the details of the trilogy (one character who shows up twice in the trilogy plays an important supporting role and I didn't even realize it until I finished the book and read reviews). I've read the trilogy three times now and it has improved with each reading. There's is so much richness to the storytelling, which I wish I could say for La Belle Sauvage. I really hope The Secret Commonwealth improves on that count.