If you look at the geometry involved, you'll quickly see why lens hoods are 'less effective' for wide angle than telephoto.
What you want is the lens to be deep in shadow. That's possible with a telephoto. But a wide angle would vignette with a deep lens hood, since the hood would cut into the image. So you see shallow hoods on wide angle lenses.
That also means that there is a narrow range of sun angles that would be outside the image, yet shaded by a lens hood. In those situations, a lens hood works great.
My 10.5 fisheye is so wide, in spite of built-in hood, that it often has the sun in the image. If not, it often has my shadow in the image!
At least it cuts some reflected glare in general.
The 18-200 hood is very much a compromise. It really is a hood designed for an 18mm lens. If you look at hoods for lenses like the 105vr macro, you will see how long/deep they can be. But the 18-200 hood is still better than not having one.
Besides increasing contrast, I find a hood helps keep stray fingers off the lens. I do have to be careful when using a circular polarizer, as you have to reach inside the hood to turn it with a finger.
If you want to see an interesting and effective lens/hood design, check out the hood on the Nikon 24-70f2.8. That lens zooms out at 24mm (lens gets longer). The hood is mounted to the body, so the front element actually moves forward significantly inside the hood when zoomed wide. This allows for a deeper hood design for the longer focal lengths.