FINALLY something on here I can chime in about with some useful information, instead of sucking you guys dry.
Replacing your screen with an HD screen could actually prove to make your display look worse. It won't be faded or have dead spots, but the weak point of most inexpensive HD displays is their ability to display an SD signal. Your nag unit doesn't send an HD signal, it sends SD, so using an SD screen will allow for accurate pixel mapping. Installing an HD screen will force it to remap each pixel, so you're at the mercy of the display. Or you might even get one that won't do the scaling and you'll get a small SD image in the center of an HD display.