I have mentioned here on this board both my anti-prop 8 activism and my work as a film producer, haven’t I? I am worried by your SN, given my sense that you are inside my head 
Just the same, I don’t see a literal retelling of the story as the way to go. Something indirect and Narnia-ish, or maybe even more indirect than that.
I think a warts-and-all biopic of Smith could be pretty interesting on several levels: as a character study, a period piece, a dramatic exploration of faith in the midst of controversy and violence, and a political commentary. Almost-kinda-sorta The Scarlet Letter meets There Will Be Blood.
What does this sentence mean? How does a book have to have cachet? What is cachet? I’m not sure what you mean by that term, but I do think Krakauer’s book has the best chance of being optioned simply because of Krakauer’s success with Into The Wild. (Is that what you meant?)
I hope so, because I think it would be the perfect book to make a movie out of. I also think Fawn Brodie’s No Man Knows My History would be good as well, but that might not be very plot driven. I haven’t read it myself, but have read a lot about it on the exmormon boards.
Also, Todd Compton’s In Sacred Loneliness might also be good. That one was all about the plural wives of JS. Might explain a lot about the mindset behind Brian David Mitchell’s kidnapping of Elizabeth Smart (convicted!).
No Man Knows My History and Rough Stone Rolling are biographies of Joseph Smith in much more exquisite detail than Under the Banner of Heaven. They both tell the entire story, one from the perspective of someone in Mormonism just begging to be excommunicated (Brodie) and one from someone in Mormonism trying feebly to rationalize his faith without concealing embarrasing facts (Richard Bushman). The info in Rough Stone Rolling is every bit as damning as in No Man Knows My History, but Bushman’s less hostile attitude means it is actually sold at LDS-owned bookstores. Any LDS biographical film about Smith is going to tell the official whitewashed story, where an independent producer would certainly use the narrarive found in the actual biographies.
In fact, what I imagine in my head is kind of comedically twinged.
Totally could never work IRL but it’s the kind of thing that makes me wish I could peak through into alternate universes to see what someone could have come up with. 
Of course humor fits the subject matter!
Oh sure, you can laugh. I’m crying.