I wouldn't question the quality of DX11 over DX9, it'd be absurd if higher level technology couldn't do better than its previous iterations, but I would question the need for what it offers. Does it really bring anything worthwhile to the table (anymore)?
It's only b/c developers are still using DX9 after so many years due to consoles. Half Life 2 was DX9.....in 2004. Thats 7 years. After that long anything is going to be in great quality.
DX11 can do more with less relatively speaking. Once the developers move to DX11 fully there will be more bells and whistles.
But, if you play a game like Crysis 2 on ultra with DX11 and hi res textures you'll see the difference.