There's definitely an XP boost for being 76 or above. On my two accounts, one got almost exactly 20% more than the other and the main difference between the two was that the one with the bonus was 76 and the one without was 75. Once the second hit 76, they also got the bonus.
That does make sense, since the penalty shrunk by 20% every 15 levels. Is 61-75 still the baseline (0.6 > 0.8 > 1.0 > 1.2) or has 76+ set a new baseline with 20% off it in chunks working backwards? I'd imagine the former, but were you paying close enough attention to notice for sure?
Why even suffer the damage and deaths from TAKING AoEs when you can just Cure all the PCs and NPCs instead and get the same reward with less "downtime" from dying?
Because you get twice the reward from curing damage you take compared to remaining unhurt and curing others. Also, being killed by a very large amount of damage is a giant pile of reward relative to the very small penalty for death. It takes a lot of mp to keep up the 1000-ish points of healing you need to do every minute to cap out your reward, and taking damage is a very easy way to reduce your healing burden.
That said, the goal is to take damage and not die. A 50-something PLD has more than enough hp to be as safe as anyone else near most AoE mobs in Campaign. It's just that death isn't something to be especially afraid of as long as you can get back up again, because you should be banking plenty of reward anyway.