yep i can tell the cleric sub get more and more useful as you level.
I dont really use the healing skills beside Recovery Division and Healing Cycle (it last 16 seconds which is quite good)
The one really useful is Bless, and it also affect all your pt members

So it can really be useful against PT giants or when PVP/Job
I'm waiting to get CLeric to lv76 so i can get Holy Spell which makes all your pt immune to pretty much every effect!!
And also like someone else said, I use the STR/Int/def buff when i'm thiefing with some friends and we encounter a big group of hunters, in that situation im quite useless as a Rogue since i cant put my DMG buff on else i get 1 hit within seconds (seems like people like to target euros first), so then I just buff people in my pt, and put Bless on, then they can even survive to mercs!
Really i'm level 78 with Rogue at 73 and Cleric at 68 (farming with 5 gap to get that one up), and I dont regret my choice at all.
When i job, i just buy 1 or 2 speed pots, and i pretty much have all the good things i would have from Bard sub from the pot.