Interesting point,
Boro. Now that I think of it, a lot of The Sil and UT was actually complemented the glimpses from LOTR quite nicely (I think the coming of Eorl to the Celebrant is one of the best examples out there), but I think that some glimpses are better left as glimpses. The thing I did not like was the structuralized, umm, how should I say it? hierarchy? organization? of the "supernatural" beings, their role in the world, and that stuff. The "macro" stuff. At first, I actually was glad to have that background, because hey, which one of us never wondered who was Gandalf really and what's out there in the West and who's that Elbereth person. Same as the age-old question of the identity of ol' Bombadil. A couple years ago I switched gears completely; things were starting to lose their magic, and the story started getting bogged down with technicalities (well, if Eru and the Valar really had XYZ powers and responsibilities, then why did they or did they not do ABC...). I think I much prefer ol' Tom as just Tom, without clarification on his origins. Likewise, I like the Valar in LOTR better than the Valar of The Silm - more mysterious, less defined, more powerful - more spiritually powerful. You hear the Elves singing of Elbereth, and you sense their awe, and you imagine stars, and a presence that made those stars - it's a lovely glimpse that enriches both the history and the spirituality of LOTR. Elbereth as the Valie who fashioned stars out of the light of the Two Trees... kinda cool, but it loses its mystery, and the richness falls apart. Debates of who is an Eruhini and who is not, and if Ents and Dwarves have an afterlife, and all those other technicalities - really, I wish I hadn't read all that because, truth be told, as curious as I am, some details are better left unknown. It's a different world where you can feel all that's meant to be felt regarding a world but that we don't feel in RL for some reason; it's not a scientific paper where everything has a cause and effect and must be explained. Some things just are. Let them be.
To bring this rant to a close, I think that one of the reason the setting of LOTR stands out from a lot of other medieval fantasy settings is that it has a good balance of definitiveness (things don't happen completely out of nowhere... except the Eagles maybe
) or mystery (magic is magic and that's the end of it - it can be felt, but not explained). Sometimes it's good not to know. Curiosity dies if it's completely satisfied, and that curiosity that you're left with after being given a small peak into the life and history of ME is what gives LOTR the richness. Answer the questions, the curiosity is gone, and so is the interest.