Your real complaint is that the Constitution is not being properly interpreted, with which I agree.
I have for a long time known it is not properly applied. Original intent is something that has left the vocabulary but for a few.
The Declaration is still a valuable documents when deciding constitutionality in light of the Constitution and Bill of Rights. That reason is it implies the intent of the Founding fathers.
Just as is done today the courts will review the speeches, discussions and debates that are part of the legislative process show the legislative intent of the bills in the mind of the passers.
The Declaration serves the same purpose.