I'm also interested in shore excursions in South America on the Mercury from Ft. Lauderdale to Rio. So I was surprised that after one month you haven't received any replies/help with your request. I had a friend who did Valparasio to Buenos Aires on Princess, so I picked his brain for that 14 day leg, but the first leg on Mercury is a new cruise and there isn't much information. We used the shore book we received from our TA and sort of guessed what we wanted to see and will change when, or if we get better information.
I knew what you wanted because I'm on the same back to back cruise, but I'm not sure most people knew what your wanted. You might ask the question again, but with the general subject title of "South American Shore Excursions"