It could be from salt, but it could also be just from the exposed aluminum corroding. Corroded aluminum can leave white powder like that. I imagine that you might fair worse with it if you live near the ocean with all that salt spray.
Honda paints the head covers, and it can peel with time, with or without salt. I don't know if it is from engine heat or what, but the right side seems to be the most common one to peel. Mine is peeling on that side too, but it's not nearly as bad as yours. Same thing happened with my Honda Magna after a number of years.
I don't have a good answer as to how to fix it unless you are really good at refinishing. I kind of like the look of the OEM finish, and I doubt that I could duplicate that brushed finish look. I am not going to buy those stick on chrome aftermarket covers to hide it. They make it a pain to remove the head covers.
I may look into just replacing them with a new set from Honda. The first set lasted 12 years. I have seen some actual head covers that have been chromed, but the prices are pretty high.
I have also been waiting for a viable alternative. Hopefully somebody will post something.