I use one on my Fuji 4229 and it makes a huge difference. It has three inputs, composite S video & Component. It outputs via a VGA connection, RGB or YUV, a 576p signal. An amazing box of tricks that improves, in my view, the picture to an amazing degree. It is however £650-700, but well worth the money particularly on plasmas that dont have the picture processing ability of the likes of the Panny and Pioneer.
If that's too much dosh then all I would suggest is find a happy medium between brightness and contrast that hides background noise without too much detail loss. Colour and sharpness I find don't need much tinkering but its a personal choice. At the very least you need to look at changing from a composite feed to S video or above. There are a number of cable solutions to enable this and its criminal to give a plasma a composite feed from DVD or indeed a SKY box.