[Galadriel55]

Originally death was meant to be a relief from "earthly pains and troubles". Elves should really be jealous of Men, in my opinion. But Morgoth convinced many men that death is bad and in their curse - basically turned it all around. I don't think that the Valar ever thought that some elves will choose to die, especially after Morgoth's lies about that subject. I won't even speculate on what Eru thought of that matter.

"For Melian, it meant that she would NEVER see Luthien again as long as the universe lasted! That is the same grief that Elrond later experienced when Arwen chose mortality."

Yes, but Elrond's situation is less severe, because a) he predicted this outcome, and b) he could take cofort in a similar story that happened before. I think that it plays a big part that Luthien was THE FIRST to choose this. And yes, I totally agree that Melian's loss is heavier than those of men, since she won't see Luthien until the world ends.
I won't call it melodrama, but rather reality like it is.