Enmity down gear has never been "irrelevant" although a lot of people neglected it in the Abyssea / Voidwatch era. That's just because they weren't very experienced in content other than Abyssea / Voidwatch. I personally never took it out of my gear because I tended to seek out the challenging events like the Provenance Caturae fights, Legion, Arch Omega, and so forth. Even before the enmity adjustments, it was possible to pull hate as a healer in those events. Honestly, I haven't even noticed the enmity changes on WHM. It feels just the same as it always has to me. For reference, here's my cure set: http://www.ffxiah.com/item-sets/94432
(It has -23 enmity, and Cure V hits for 1125.)
As far as enmity efficiency, Cure V is the most efficient in terms of enmity. So don't stop casting that. However, whereas Cure V also used to be the most MP-efficient, that is no longer true. Cure III is much more MP-efficient now due to the healing skill changes. So for that reason, the lower Cures are much more valuable than they used to be. Basically, use whatever Cure is right for the job. I haven't stopped using Cure IV as a result of the enmity changes, and it hasn't caused me problems yet.
As far as PDT/MDT, it's never been much of an option for me. For one thing I rarely die even if I do pull hate, I can tank most endgame stuff just by blasting Cures on myself. I'm Elvaan though, so take it with a grain of salt. There's also the fact that I don't use Spellcast because I think it slows WHM down, and thus my precast set is my idle set. Having to squeeze both refresh and fast cast into the same set of gear doesn't leave much room for PDT as well. So I just stick with curebombing myself if I somehow pull hate, because I rarely have hate for long.