Malfunctioning, scuffed, U.V damage or cracked; whatever the problem with the instrument assembly it is difficult (usually impossible) to rectify.
Fitting new replacements will restore the appearance of this area of the machine. And it is this area that you are mostly aware of as the rider. Scruffy, malfunctioning instruments (and controls for that matter) are just annoying on the eye and the brain!
Related components you may wish to consider: