Knowing for sure doesn't actually matter here. The problem is with singling out a single target from a universe of alternatives, and then justifying the choice of that target with an argument that can just as readily be used to justify any of the alternatives.
Just to highlight the difficulty, imagine someone arguing that if God exists you should read "Mein Kampf," because even if there's only a very small chance that God wrote it, you can't be sure He didn't, and the cost of reading it is low, and there's a high potential payoff, and reading it would help establish authorship.
I expect you don't find that argument compelling, even though it's the same argument you cite here. So if you find that argument compelling as applied to the Bible, I expect that's because you're attributing other attributes to the Bible that you haven't mentioned here.
I didn't say "read the bible" would be compelling, I said it would be good advice. "Stop doing heroin" is good advice for a destructive heroin addict, but unlikely to be followed.
By "God" I mean "the all powerful being who flung Adam and Eve from Eden, spoke to Abraham, fathered Jesus, etc., etc., etc.", as is the common meaning of "God" in our culture. Had I said "god" things would have been different. As it is, I think we can say that, if God existed, he wrote the bible, and that my injunction would be better advice than the Mein Kampf advice.
3rd May 2014: I no longer hold the ideas in this article. IsaacLewis2013 had fallen into something of an affective death spiral around 'evolution' and self-organising systems. That said, I do still hold with my statement at the time that this is 'as one interesting framework for viewing such topics'.
I've recently been reading up on some of the old ideas from cybernetics and self-organisation, in particular Miller's Living Systems theory, and writing up my thoughts on my blog.
My latest article might be of interest to LessWrongers - I write about the relationship between life, purpose, and intelligence.
My thesis is basically: