Hi
Unfortunately, pushing the sharpness will mean that you lose a lot of detail and end up with ugly halos around things.
If you are using Photoshop then there is a filter called "Add Noise" that will do a nice job. You can find it under Filters > Noise > Add Noise
Experiment to see whether the Uniform, Gaussian, and Monochromatic options give you the best result. I'd also suggest copying the layer before you try this out so that you can go back to the original if it all goes horribly wrong.
Enjoy
J