I like the idea's posted by the OP, trough the MP consumption is basically nonexistent if its just 10mp/sec for both fairies. A Healer with at ilvl510 with ~1800 Piety regenerates arround 400-500 Mana every 5 seconds so the MP consumption would need to be alot higher than that or penalized in another way, like draining Fairy Gauge instead.