If i already have skyrim and i buy legendary skyrim what happpens?

can i get all the dlc? is the basegame of the legendary edition wasted? or am i just upgraded

I think you should get an extra copy of Skyrim in your gift inventory. I am not sure but it would be only logical. You could ask steam support directly

If you do get an extra copy you should gift one to me ;) 

I'm 90% certain a new game will be added to your Steam library titled something along the lines of "The Elder Scrolls V: Skyrim - Game of the Year Edition."

I know from personal experience that you won't get a new copy in your inventory or whatever.  Sorry, I thought I would get a second copy of a game when I bought the Ultimate addition just like you :(