We agree that Jackson's Hobbit suffers from too much of the wrong sort of embellishment, but I think, in an episodic format, The Hobbit could be much longer, with a slower pace, and capture the feeling of the original book much better. Same with the LotR.
RoP has a similar issue, IMO. It's a retelling of a story which takes place over thousands of years in the appendices and for which Tolkien wrote enough detail to outline the major plot points. The writers of the show have gutted much of that framework and filled it in with details that aren’t needed for the original story: things like the whole Southlands subplot, the Stranger/Nori subplot, the idea that anyone was ever "hunting" for Sauron, and the idea that mithril would have anything to do with slowing the fading of the elves. Jackson’s LotR has some insertions of this type, mostly pulled from the appendices, but is more noted for what was cut rather than what was added.
Of course the story of Beren and Luthien is written out in greater detail than the material in the appendices from which the show draws, but that just means there would be less detail to add. I don’t think having that level of detail would prevent the introduction of subplots or other embellishments to expand the existing story. Drawing some of those details from other parts of the Silmarillion would, of course, add grist to the mill.
