I'm still on the fence with PI it seems to be designed around the WHM potentially healing more then one person with Cure/Cure2? It's certainly a confusing spell, it does work though, and is a pretty fast heal, but I've only used it in the two level 70 dungeons so far. It would be nicer if it proc'd on the WHM instead and potentially showed up on the Lily Gauge.
As for lily system in all honesty it feels like SE didn't even care, they got everyone else setup with a resource system and got to WHM and was like "meh, this will do". It's not a terrible system, but there is no feeling of lose whenever I run stuff without access to it at all.
-Give a Bonus to having Lilies up, healing/spellspeed or something, potentially have it increase confession procs too.
-Let lilies affect more spells, Presence of Mind, Benidiction, and Thin Air, maybe even role skills if that's not too unbalanced.
-Not lily related but job specific, get rid of Fluid Aura and Repose, give WHM's something else.