On Hypalon and Neoprene boats, surface coatings can restore abraision damage. Just don't mistake the general breakdown of the coating for abraision. No surface coat is effective when the inside coating has broken down--and that is the most common reason for the demise of old rafts.
It rarely happens when the Hypalon content is high--like 80% as on the grey Riken rafts, but is common on rafts with high Neoprene content--like the blue or red Rikens. We've all seen the symptoms: The surface starts to look chalky, then it starts to check and crack. Pretty soon, air seeps through in large patches. At that point, the raft is finished. No exterior coating can hold the air in.
I've tried using an interior coating with mixed results. It works where it sticks, but the trick is getting the liquid material all over the inside of the tubes. You mix the two parts, squirt the liquid into the raft, and then fully invlate it. You and a couple of friends then lift the raft and keep turning it over and over in every direction until the liquid gels. You'll see it start seeping through the bad spots, sealing from the inside. To that extent, it works.
The problem is that it is almost impossible to get full coverage, and if you stop turning the raft too soon, it pools and makes thick spots that are semi-stiff and tend to crack. Also, don't deflate the raft for several days after treatment, or you might get adhesions.