Aye, the Letters are interesting in not only providing some commentary from Tolkien, post-LOTR, but just thoughts about world affairs, other books, authors...etc.
I caution when using Letters to determine some new, hidden information about Tolkien's story, though. Tolkien admits when responding to fans' questions, a lot of what he wrote could have been as long as 30-40 years ago, so he may misremember something, or what he consciously reflects upon after having written the story might be completely different. That's not so much of a problem with Letters, more a note-to-self when reading them. Personally, I find the stuff in Letters more interesting then reading his early draft material, but that's just individual preference.
