RB: The traces will need to be vectorized later so the lower original resolution doesn't really matter much as long as the quality is good enough to vectorize.

Sean: Yeah, you'll need a scanner with a good depth of field for that to work well, you'll definitely need a CCD scanner instead of a CIS one.
Of course if the plastic is scratched that won't really help much and if you can get to scan the LCD directly will certainly render better results.