I did something similar for my half-elves, and are considering doing it for my half-orcs. (Half-races are not popular around here; we tend to go with Shadowrun's ideas of racial idea that they are magical archetypes).
Half-Orcs would become Hobgoblins, pure and simple. Hobgoblins have the potential to be a civilized, player-worthy race, and a bonus to Dex just doesn't sit well with me as an orcish trait.
The half-elf is a mirror-image of the shadar-kai, humans that got caught in the Feywild and adapted to it.
Half Elves are not strictly a crossbreed between human or elf, tough many of them carry a bit of elven blood. Instead, they are humans who have been infused with the essence of the Feywild. Sometimes called changelings or feytouched, they are not completely at home in either world.
Half elves are descended from humans who stumbled into or lived in close proximity the Feywild. Some have ancestors who moved to the feywild seeking new lands, others were abducted as slaves or victims of trickery. Some are human children raised by fey foster parents. Once in this strange new world their human sensibilities failed to help them, forcing them to develop a wider range of skills and a more fantastic mindset. Yet they keep their human ancestor's appreciation of and ability to exploit wonders. A half elf is rarely fazed by the amazing sights of the Feywild, but they are more impressed by them than most fey, who take such things for granted.
Half Elves have their own communities or live on the fringe of human or eladrin settlements. They are friendly to strangers and tend to adopt humans coming to them singly or in small groups, there is always a need of more reliable allies. Their settlements are usually outposts, safe havens in the wilderness, either hidden or in inaccessible places relying on their position for safety. Sometimes such settlements grow into towns or small cities, but they rarely develop the might of human castles or the grandeur of eladrin palaces. Half-elves often mind inns, trading outposts, ports of call, mountain cabins, lighthouses, and other wayfarer settlements. Many half-elves are merchants, being more practical than fey and less hidebound and parochial than humans.
In the mundane world, half-elves tend to live on the fringes of human society. Their wild fey blood calls out to them, making it hard to settle permanently in civilized areas. In the Feywild, Half Elves live like humans on the ultimate frontier; always exploring, always willing to adapt, but also keeping a lifeline back to civilization.
I usually go about it a little more free form. The player can decide the RP stuff to fit into the world any way that they like. Then they can decide on any "racial" game mechanics benefits package that they like. It is interesting to see a reskin that is set in stone for the campaign instead of a case by case basis. I like your races, particularly the Eldar. I have been contemplating a goblin/elf fusion race that is more folklorish than Tolkein's elves, and some of what you have is basically what I was thinking. Nice.
