'87 325is ~200k miles

I am going to replace my muffler, has some holes, really loud, probably have a shop do it. In checking out the muffler I looked at the catalytic converter. I tapped on it, shook it, and don't have any noticeable rattle. There is no noticeable loss of power either.

There is a metallic rattle noise when I give the car gas that lingers for a bit but goes away if I get off the gas, or so it seems. Listening to where it comes from it seems from the engine bay, valve cover area. So I think it is that. All heat shields seem secure.

Long story short, the outside covering of the cat is gone in about a 4 inch diameter circle on the center bottom of it, exposing the darker metal, past the asbestos. There is also some other rusting of this same cover metal at where the pipes branch off.

Should I be concerned, meaning will it help to patch somehow or install of cover of a sort for that portion of the missing outer cover to help prevent a hole from happening in the cat? Or is that outer metal just a heat shield in a sense and the exposed inner metal is ok?

I am trying to not spend money on a new cat until I really need to.

Thanks a lot