Is there any benefit to purchasing this lens for my Nikon camera?

I have a Nikon D200. I have an AF 18-250 mm macro zoom lens…
I was thinking about purchasing a Nikon 85mm f/1.8D lens.
Would there be any benefit to this or would my pictures turn out the same as because 85mm is already within the 18-250 mm range?
My goal is to take beautiful portraits with blurred backgrounds.
I'm obviously not professional. I'm willing to spend as much money as possible though to get the best overall portrait results! So if you would recommend something else, let me know.

The aperture values on the 85mm would mean you'd get much more blur in your photos. "Fixed" lenses, as they are called, are often used by portrait photographers. Bear in mind you will have to be comfortable with manually focusing the lens due to the fact most fixed lenses only have Manual and Manual Priority Automatic modes and no Fully Automatic focusing options.

A macro lens blurs as I'm sure you know as it works with your depth of field. That can also be achieved with any lens if you know how to adjust your settings for depth of field. However the difference is a Macro lens will always do that with pictures the other lens does clear shots as well.

A macro lens is for a specific type of photo the other lens has the ability to do more then a macro lens does.

The 85 f/1.8 has a MUCH larger aperture than the 18-250, meaning at 85mm on both lenses, the f/1.8 will have much more background blur and also appear more bright. This means you can put the iso down, resulting in less grain in your images.fixed focal length lenses (or prime lenses) also tend to be sharper, and especially sharper than lenses that have a massive zoom range like the 18-250. If you do end up buying the 85 f/1.8, take the same picture with both lenses (at 85mm) and you'll see the difference in background blur and sharpness.

Without specifics, I'm guessing that the max aperture on your zoom at 85mm is f4. The f1.8 would give you 2 stops more light and shallow depth of field. So yes it would blur the background more. However it would be a razor thin focus point that might not give you enough depth where the entire face is in focus. There are other variables to consider, sensor size also plays a role in DOF.