As far as I can see, and I may be wrong, this idea is utterly sterile.
By this I mean, the DH doesn't lead to anything. It bears no fruit. If you begin to think seriously about it, it will not lead you to think seriously about other things. Books on the DH all seem to start and finish with the DH. Those who take the DH seriously make claims like 'it is no longer possible to read the Pentateuch as a unity' - something which is manifestly untrue, since these books have been and still are the subjects of expository preaching and teaching all over the world. The DH doesn't help you to understand, but in fact makes the Pentateuch impossible to comprehend at all.
It got me thinking: what makes an idea sterile? How can we spot the ideas which are likely to become hopelessly self-referential and curved in on themselves, like the DH? Ideally, how do we spot them before we invest too much time and effort in them? I had a few thoughts.
1. Is it possible for this idea to be firmly established? The DH cannot be firmly established, dealing as it does with subjectivities and the attempt to get behind the text into unseen precursors. The result is that arguments go back and forth over its validity, or the precise form it ought to take, without any real conclusions being possible. It can be talked about forever, and we will never be able to view it as settled and move on. So it is sterile. What other ideas might be like that?
2. How many layers of hypothesis are there between the acknowledged facts and the conclusion? The DH has all the features of a cloud-castle. Layer after layer of supposition, sprinkled with interim conclusions that make good sense if and only if you accept the previous hypothesis. This gives lots to talk about that isn't really the substance, and keeps the idea in the conversation without it really having anything to say. Sterility. How much theological and philosophical construction works in the same way?
3. Can the idea be rephrased or summarised in a way which would be useful to the average chap on the street (or in this case, the average church-goer)? This isn't totally foolproof, but I think it is a warning sign to us if our ideas are useless for living. It's a potential sign that they are sterile ideas. I'm guessing quite a lot of thought falls under this heading.
Any other ideas?