I have the 50mm and did look at the 35mm to compliment it, but I just couldn't justify the close focal length between the two.
I'm now looking at the 28mm f/1.8 instead as in my opinion it's a better seperation between the two.
If you've got the 35mm, then maybe look at the 85mm instead of the 50mm and see how that looks.
Another quick test you can do (if it's not already been mentioned), is put your 18-55mm lens on and focus at 35mm & 50mm to see what view you're getting.
I'm now looking at the 28mm f/1.8 instead as in my opinion it's a better seperation between the two.
If you've got the 35mm, then maybe look at the 85mm instead of the 50mm and see how that looks.
Another quick test you can do (if it's not already been mentioned), is put your 18-55mm lens on and focus at 35mm & 50mm to see what view you're getting.