Oh yeah, I forgot about Bonds
Immaterial is a big deal, I wouldnt remove it, or you'd get situational Vulture (that cant find its place in any competitive deck). Instead, I would suggest growth based on amount healed / 5 or something like that.
IMO, something like this must be a big threat, as you cant really force your opponent to heal (well, there's AM on your own creatures, but then you're spending loads of quanta and cards to set it up).
OR it has to have silly cost like Purify (even though Purify is still hardly ever used).