YES! I totally would. We were there around then this past year (2017) and it felt really busy, even though the days weren't supposedly that busy via crowd predictors. Maxpass wasn't rolled out yet, but we realllly wish it had been.
That said, I don't think we would have needed it for California Adventure. The big ticket attraction in Carsland we were able to do a paper fastpass on and otherwise waits were reasonable over there. Maybe prioritize it for
Disneyland days?