Hayden Christiansen as Glorfindel? Never!
Joaquin Phoenix as a son of Feanor... I think he would make a perfect Maglor, except the eyebrows...
I agree that elves of the same generation should be casted with actors about the same age.
As for Lúthien, absolutely no Angelina Jolie or Natalie Portman (too human-looking) or Keira Knightley (a poor actress, though beautiful).
Alan Rickman as... Eöl! xD