As a Plat, the only times I've ever gotten upgrades EWR-SFO or SFO-EWR are very early Saturday or Sunday morning (flythis route 1-3 times a month). I have noticed in the past few months that upgrades (1-2 total per flight) have happened for those on higher fares than me as where it used to be none per flight.

As far as the 753 vs. the 738, the seats are exactly the same, not sure about the AVOD.