Definitely worth it to upgrade if you can. It is one of the longer flights (excluding the SYD and YYZ-HKG flights) just down to SCL, and this doesn't count the hop over to EZE. The pods are decent for sleeping.

As far as ability, you are fortunately flying outside of high peak season but the route is pretty busy in J. I'd suggest not giving up your cert in LAX unless they can upgrade you for the whole flight. Coming back, you either will get upgraded or not right at the start. Definitely worthy of an SSWU.