My L710 dome drivers didn't have the dent nor the mottled finish. I had them rebuilt and the sound quality is definitely improved. So there is time based degradation of these drivers that you can't necessarily see. I think it is evaporation of the ferrofluid inside the dome layers that is the main contributor to sound degradation.
Edited to add, if you find the sound no different from the other mid and you're enjoying that sound, then likely no urgency to have them rebuilt.
@Newmcdaddy, It doesn't necassarily affect the frequency response as much as it will affect the distribution of the sound produced.
According to Richard So, ADS repair emeritus, he no longer has repair parts for the dome midrange drivers and rebuilds them using salvaged parts. He has redoped the fabric domes and rebuilt the voice coils by hand, but keep in mind...he's getting old and who knows how much longer he'll continue to do repairs.
The grill got pushed in against the dome. Send both mids to Richard So. He will remove, and clean the domes, and recoat them with the sticky dome goop. They will look new. I say both so they will have equal output.