Was buying this lens a mistake?

I have a Nikon D5000 body and an 18-200mm f3.5-5.6 lens. I just bought the Nikkor 105mm f2.8 lens, mainly for macro work. Firstly, isn't the 105mm covered by my 18-200mm anyway? I just can't seem to do any insect or flower work with the 18-200mm. I'm also concerned that i've paid almost $1000 for the 105mm lens and it's not going to give me any better photos than the lens I have.

Added (1). As of yet, I do not have the lens to play or practice with. I have been tipped off that it is being given to me as a Christmas present.

18-200mm is an excellent walk around lens, much better than 18-55mm and 55-200mm combined. You can put it on a camera and get good landscape images and portraits.

105mm is a prime lens especially designed for macro work. You will get stunning macro results from that lens.

Yes, at 105mm, there's an overlap in the focal length between the two lenses but so what? Both are being used for different purposes.

What the other users said is true. There's also the difference in aperture. The f2.8 lens means it is fast glass. With a 2.8 aperture, in a dimly lit environment you might be able to photograph at 1/100, 400 ISO, with your normal lens you might only be able to photograph at f4.6, 1/50, 800 ISO. (Those numbers are just guesses.)

Whether it was a mistake or not, depends on whether you make good use of the lens or not. The lens should be able to give you higher quality images than what you have been getting.

In the future, before you make big investments I suggest researching a lot and getting others opinions before you make the big purchase.

Not a mistake at all.

The 18-200 mm lens is used for totally different reasons than the 105 mm macro.

The prime 105 mm macro lens will always have the potential of providing you with better images, if you are up to the task.

The time it takes to learn how to get the maximum usage from any lens may be three to five years. By then you will understand why having both is not a mistake, but rather a good plan.