Regardless of what the authors intended, I don't think it can be taken literally or as an inerrant whole. Parts of it, like the genealogies and the detailed instructions about animal sacrifice, may have some historical value in understanding the ancient Hebrews. Other parts, like the horrendous accounts of divinely inspired massacres of innocents, reveal values that must be rejected on the basis of other values of justice and love that are found in the more inspiring passages of the Bible. Still others, like Genesis, Job and Ecclesiastes are profoundly allegorical, and anyone who takes them literally misses the point. I owe my Christian faith to Genesis, but think it would be absurd to take it literally. There were many authors, not to mention redactors, with many different agendas.
I've always found this to be the most ridiculous bible story. At least the others have some form of mysticism involved. This is something tangible - a monsterous boat carrying a pair of every species through a massive flood. Something that could clearly never happen. It's totally absurd, and even taken as symbolism it means very little except that god is rather a crabby bastard, which we'd already gathered.
Is it a matter of choice which bits you take literally? You seem to be saying that the bits of the bible you don't like, or the bits that very obviously don't adhere to physical law, should be seen as symbols. Just a few people can come up with a hundred interpretions for a single text backed up by evidence from the source, making the bible's usefulness as a guide for life very limited indeed. I particularly enjoy the poems of Keats for example. I feel their symbolism has deep messages about the nature of life and death, yet I would not claim to base my lifestyle on them or call myself a Keatsian. Some read the poems and are left cold. Others think they're just pretty. Some see messages I can't, and some think my interpretation is nonsense. The fact is I accept that it's just literature, written by a human being no greater than me or anyone else, which may be worthless to some and of some value to others, yet doesn't hold any divine truths that only I can see. You seem to know that the bible is just another human story, so why call yourself a christian just because you appreciate many parts of the text and reject others just as you would with almost any other book, including other "holy" books?
"Yay Noah! You saved all the animals, humans woohoo! What would animals do without us? We're number one, the best! Go HUMANS!" "Noah, fuck yeah! Coming again to save the mother-fucking world yeah!" -Homo Sapiens cheersquad