W600 Purchase of a lifetime (for me)! Would you restore?

I agree with others to keep them as original as possible, as with anything vintage, but removing the mold will definitely be necessary. Those black spots are definitely mold/mildew and while it looks dormant it is very much alive. If not treated it will continue to get worse and eventually overtake the entire card area. I had a vintage title to an antique car I have and in the course of two years it completely covered the document rendering it worthless. I had made a copy of course but the original was lost forever. I would also have a professional do it. There are several good ones out there.