Never found much use for Improved Healing IV even though I have it. I cast about one Tnarg's for every 40 Queiscences. Quiescence is cheaper, heals for more (with extended blessing and scrm, it lasts 8 ticks, 420x8 = 3360 and in my case with quick buff 3, casts faster. Being heal over time, it allows you to not worry about healing all the time too.