If I have a 18-55mm lens, is there a point in buying a 35mm prime lens?
Should I consider 35mm or instead buy a 55-200mm for better range?
A similar question about a fast zoom lens rather than the kit zoom: Would a prime be redundant with a fast zoom?, and also somewhat related (because it's basically the _opposite_ question): Getting ready to buy an entry-level dSLR — should I skip the kit lens?
The first lens I bought was a Nikon 35mm f1.8 DX. I bought mine because the kit lens (18-55) required me to use a flash for indoor, low light pictures. Since I'm the 'family photographer' and need to capture all the birthday parties, reunions, graduations, funerals... I needed a low light lens. The 35mm f1.8 is still the go to lens for family events, day or night. I now have a 50mm 1.4D, which is pretty awesome too, but for indoor, around the table pics, it's a trifle too long. If you're interested in outdoor, good light pictures, then the 55-200 will probably be a better choice.
I bought the 35mm f1.8 DX for the same reason as Therealstubot.. and while I use it a lot indoors, it's almost always with a bounced flash anyway. Unless you live in a very bright house, don't think a fast prime is enough to shoot without a flash - unless you are happy with ISO occasionally ranging into 3200-6400 range. The only real reason I use the 35mm is for shallow DOF (at least, shallower than the kit lens allows).
Yes. Prime lenses usually offer both superior image quality and larger apertures compared to zoom lenses of similar price. This is due to simpler mechanical construction, as less moving parts are needed, and due to especially chromatic aberration being easier to correct for just one focal length.
The decision between 35mm and 55-200mm is in the end about your needs - 35mm lens gets you close to the 50mm-on-full-frame that has often been considered as the "neutral" focal length, and the one to use if you need to pick just one. Also, fast prime gives you ability to shoot concerts and other performances, and different kinds of indoor events in general.
55-200mm gives you more reach, and can be useful if you want to capture small details outdoors, or get perspective flattened up.
I'd add that having tried both 35/1.8 and 55-200/4-5.6 I must admit 35/1.8 gives noticeably crispier picture, which in turn allows for tighter cropping, making it comparable in reaching power to the 55-200.
Having both, I strongly disagree. First of all the 55-200 is definetely sharp, a worse maybe than the 35mm but not by much. Also, on cropped sensors, a 35mm lens angle of view is 44.7°, at 55mm it is 29.38°. This would mean that the image would be cropped approx by 2/3 on both sides, and on a D50 that would be a 2.6Mpix image (pretty low). And to get the same image you'd get at 200mm you must crop a 200Kpix part which would be completely useless.