I feel strongly that we miss much when we fail to realize how the First Vision and the Book of Mormon were used in the early days of the Church within missionary work.
When the Book of Mormon was used as the launching pad, as the catalyst in and of itself for an initial spiritual experience ("Here's Moroni's promise. Read this book from cover to cover with that promise in mind. Follow that promise. THEN, when you've done that, we'll start teaching doctrine."), missionary work flourished the most. When we started using the Book of Mormon as a doctrinal proof-text and started focusing on teaching doctrine over converting spiritual experience, missionary work flourished the least.
The structure of the Book of Mormon (especially Moroni 10:3-5 - all three verses, not just the last two, which now are used as the Seminary scripture mastery passage) is laid out in such a way to inspire people who read it to believe that God can and will speak to them (let them know the truth of all things) - and to have such a recognition subsequently allow them to read the Bible and understand and believe what it really says (primarily about God, their relationship to God and what the "power of godliness" really entails). Iow, the Book of Mormon allows people to read the Bible with "new spiritual eyes" through which the "mists of darkness" caused by centuries of bad Christian doctrine and apologetics can be overcome and people can understand who they really are.
I love the way Preach My Gospel is structured, and I love the flexibility it is supposed to provide for the teaching of doctrine, but I think we miss the mark when we don't use the Book of Mormon in the way that I believe it was intended to be used - when we make the First Vision the keystone of our religion. (I don't want to dismiss the First Vision in any way, but it's important to understand that everyone and their dog were having spiritual experiences during that time period in that geographic area; the Book of Mormon, on the other hand, is unique.)