Well, as one who could have said it, I think it always needs discussion due to the abuse of people in the usage of the language of the Declaration.
To explain my position, I refer to the Declaration as an "Animating" document and to the Constitution as a "Framing" document. Certainly they were both essential in our "founding."
The former was a letter to the world and a communication establishing what animated our actions and clearly established who we thought we were. It was created by representatives, but not confirmed by representatives after a full review by the people. It was not meant to be law or to replace aspects of established common law.
The Constitution was meant to be Law and very stringent and supreme in nature. It was approved by the people through their representative state governments.
Why is the distinction so important in political discourse? In my opinion, it is because much of Collectivism tries to stick its nose under the tent of our system of government by using the words of the "animating" documents. Letters by Jefferson, quotes from pamphletiers, and the Declaration's communicative wording all are fodder for the Rationalistic Totalitarian Democary activist.
Once the nose is in the tent, Equality, displaces property. Liberty becomes a limitless god and lawful order is just a convienience when needed by the Rationalist. And lastly, the Framing document is found to be "deficient" for not meeting the expectations of the "animating" document as determined by the Rationalist. A Crisis looms and only the vision of the annointed with the force of centralized control can save the issue-made-god. (See T. Sowell)
Your shunt to discuss what founded the framing document is worthy of discussion, I would agree. But the issue that "animated" your post is never to simple to avoid in detail.
For those who have the time, I reccommend Forrest McDonald's Novus Ordo Seclorum,The Intellectual Origins of the Constitution
It [the Constitution] was approved by the people through their representative state governments.
The actual approval was done by ratifying conventions that were chosen directly by the people, bypassing the state governments.