AddeRabbi brings up a clever point. That Nes-Nisayon Theory (NN Theory) can also be used to answer the question of why the Torah looks like it was written by 4 authors and a redactor. And also I guess why some pieces appear to have been written late, about 500 BCE.
However I think you need to hold of NN-Theory even without the problem of Biblical Criticism. How so ? Let me explain.
If you were to compare my blog with Shakespeare, it should be pretty evident who is the better author (No, not me silly !). So, likewise, shouldn't the book that G-d wrote be the most amazing book you ever read ? However even the chazal / gedolim (there is a great quote from someone about the goyim having better books than the Torah - can't remember where) will admit that on the outside, it reads like a fairly typical work of that era. Obviously it has deep secrets etc. according to chazal, but I am just talking about the external form.
Now, why wouldn't G-d create a work, which was obviously the work of G-d ? The 'decision' to make it appear human made must have been a 'conscious' decision. Even saying that it really is amazing but we are not on the level to comprehend its amazingness doesn't really help, because Hashem could have created a book which we were able to comprehend as being amazing.
So the only answer is that it was written as a human style work as a nissayon. Because if it was obviously the work of G-d, we would lose our bechirah. So, even without the whole business of higher criticism, we still need NN-Theory to explain why the Torah just reads like an ancient babylonian text, and not the word of G-d.
And really, this whole question just reduces to the question of why doesn't G-d appear to us again, why is he hidden. Must be a nisayon. So you need NN-Theory after all. In which case, you might as well go whole hog and accept Gosse after all.
Oh dear. And Good Shabbos.