No experience with Kevlar in tires, but it was the dilemma when I was buying canoe to carry on roof of my TC.
Fiberglass or plastic canoe weights about 90 lb for 16' size, what seem light for me at the time, till I tried to carry it 1/3 mile to the lake.
Finally I was able to find used Wenonah canoe, who build with Kevlar makes just above 40 lb. Whole World of difference in this application.
Coming to tires, don't think couple of lb difference will be worth the top dollars for average user, but some buyers might go for it.
Rocks will damage the rubber before they damage the reinforcement, so I don't see how that might affect your use?