OP Here. Update.
I offered $385 pp for the redeye LAX-LIM (787) on a Friday night and got the upgrade for me and husband.
Offered $360 + taxes for LIM-LAX and we didn't get it. Not too disappointed as it was a day flight.
First time in economy on LATAM's 787. Not bad (I am 6 ft tall) but the seats are indeed very narrow. I would fly it again with no hesitation despite being bumped by FAs or pax walking by once in a while (aisle seat).
P.S. I have no status with LATAM.