So, I went ahead and removed the port side chain plates as well. I've got three halyards up supporting the mast (I live at the end of protected canal, very little boat movement). All are at a shop being replaced currently. None of mine looked like those scary pictures that you see others post where they have either failed or are very near failure. On both sides, the triangular plate (aft lower) looked worst, with a few hairline cracks starting to show. I probably could have went without replacing the other four, but better safe than sorry, especially after all the trouble to get them out (it's really not that bad). I am going to go ahead and do the forestay and backstay plates after I get these new ones installed.
One thing I did find that is of note (see pictures below). There was a thin piece of trim wood behind the aft and cap shroud plates that had deteriorated due to past water coming in at some point in the life of the boat before I was the owner. It had been found during my initial survey, but we had determined it was trim with solid good bulkhead behind. Well, once the chainplates were removed, I examined it more closely and determined it could simply be pulled out, which I did. I am going to have it replaced with an aluminum backing plate to keep the chain plates in the same place and add strength. I found an old post (link below), where it looks like this has been done on other boats as well. You can also see in the picture below what happens to the chain plate bolts over time as they retightened themselves in their holes, shifted, and bent under load as that piece of trim wood deteriorated. Certainly something that would have become a problem in the long run.
viewtopic.php?f=5&t=894&hilit=backing+plate