What do you want to take pictures of? bugs? flowers?
How far do you want to be from your subject?
So far it sounds to me you have no reason to buy one. If you need to ask why you should get one it's obvious the need does not exist.
OK, what is a "reversing ring"?
A reversing ring screws into the filter threads and allows one to turn the lens around and mount it to the camera. You have to focus by moving the camera...it is a crude way of getting into "macro" photography. Below is a link to reversing rings from B&H Camera.
A macro lens allows you to focus closer. A lot of lenses like the old Nikon 28-105 and new Nikon 18-200VR have a "macro" capability. Usually they let you focus close enough to obtain a ratio of 1:3 or 1:2. That means the image on the sensor is actually 1/3 or 1/2 life size. You can get an even larger 1:1 image on the sensor using a "normal" lens with a bellows setup, reversing rings, or with a dedicated macro lens. Some "macro" lenses only focus to 1:2, so you need to check before you buy. See this write-up for more details. http://en.wikipedia.org/wiki/Macro_photographyWell, I find life easier when I use the right tool for the right job. I have pounded in nails with a wrench before. It worked, but it was not an elegant solution. When I got a hammer pounding nails was easier.
Since I am taking Macro shots, it makes sense that I get a macro lens, but I am still not sure why a macro lens is a more elegant solution.
Is the macro going to give me more depth of field?, faster lens?, more detail?
Can I get closer to the target?