You could try fixing the chips with either joint compound or wood filler--maybe even some of that epoxy filler they have these days. All can be smoothed down to get the profile to match what is there, and then painted.

Plaster of Paris or patching plaster may do the tricks for your corbel. Use a wash coat of thinned elmers glue to bond the new to old.
If you get a glob to stick, you can work it to shape once its dry with sandpaper.
For the terrazzo, maybe an masonry epoxy filler from the people at Abatron.