I highly recommend the upgrade to C+ seats, on the overnight flights to and from South America. I think it is well worth it. If you book early enough, you can get the bulkhead seats with even more legroom*. For now, the upgrade is still an add-on for deep South America flights, which means you can buy it per segment, even on award tickets. I don't think there is even an OPTION to buy it on the domestic segments, currently. So, hopefully, you can get an exit row on those.

*except the 767-400 which has ok legroom but not massive legroom.