While the resolution is often worthless, the nice thing about the 4k Blu ray standard is the increased color depth. Less banding is always good.
Yes, massively increased colour gamut and dynamic range make it worthwhile, regardless of how you feel about resolution increases.
Yes, emulsion scratches are usually green, can be other colours depending on the depth of the scratch, base scratches are usually white if clean, or black once they get dirt in them.