Should I buy this lens?

Should I buy this lens? Will I use it? I think I need it, but I have lived without it so far I feel like I need a new lens though and I can't spend a lot right now. I just need some variety. I already have some pretty good zoom.
http://www.adorama.com/NK5018AFDU.html

p.s. I won't necessarily buy it here, I just needed a link. I'll probably buy locally.

The length is what I am not sure about. I really don't know which would be more useful.
I was guessing the 50 since I would use it for weddings.

Is the focus hard to nail so wide open? I know these are such basic questions, but I haven't expanded my lens repertoire much. Keep in mind I have to use auto focus. I, uh, have vision limitations

Ok, just flipped through my last session in Bridge to see. It was a combo studio/outdoor shoot.
Most studio stuff was 45-50 if it was full length. I zoomed in for closeups, but I could move closer.

The outdoor portion was decieving, not my normal way of shooting. It was dark and rainy, so I got in close so my aperature could open all the way, so I shot around 30. When I have more light I use a much longer length to throw the background out of focus, which I wouldn't have to do with a 1.8 lens.
Right?

My all-purpose lens is 18-135mm (kit lens, but I like the range), I can open it up to 3.5, which I do often. I have a longer lens, up to 200mm, but I rarely put it on my camera. I don't shoot wildlife or anything that requires me to be a distance.
 

The 50mm 1.8 or the 35mm are both top end glass, cheap because they are simple not because of the components. The 35mm is a newer lens, might have a faster motor in it.
It is one of Nikon's most popular lenses. Sigma makes a 35mm EX as well. Google reviews and pick the one that "they" like best.

That little prime lens will blow you away how sharp the images are compared to your zoom.

Yeah I think it will be a good addition to help give more variety to what I can do, and it's a small investment and yeah, I didn't think about it being a small lightweight lens to carry, that will be nice.

Actually it's not late at all Robert, I haven't purchased it yet. I know it's not expensive, but I still need to wait a little longer until I can pay for it.
I am glad to know you get a lot of use out of it.