I don't like being a Vampire that much. Every Magicka character I play does absolutely fine without it while at the same time 99% of the Magicka players I see (ab)use it.
Depends what you wanna do. Anywhere you're gonna end up having to Purge spam (vHoF, vAS, vMoL) you'll probably want the extra regen. But it's not gonna make or break you in most cases.
None of my healers are vamps but so far I haven't had any issues with sustain. But I don't do trials either so I don't know if that content is more demanding resource wise.
Honestly it's in between yes and doesn't matter.
Mist form is actually nice for Kiting in vAS and is also the only source of mobility for a Templar in PvP. In other trials if you stay on stage 2 the increased regeneration is nice and the fire damage not an issue.
Pain-Healer - Argonian Templar Healer (EP) - Immortal Redeemer - Gryphon's Heart
Guild : Ghosts and GoblinsTarget Dummies
Players know me as Jeban
If your CP is high enough is far better to have it. You do not even notice the fire damage but you will notice you are more squishy in pvp from certain skills.
If you are low CP, forget it, so many things will just one shot you if you do not know the pve content mechanics or in pvp.
I have 3 healers atm and only one is a vampire. Aside from not being able to use Mist in pvp, I genuinely don't see any disadvantage to being a non-vamp healer.
The vamp mag regen for healers isn't that essential of a bonus since you should already be managing your mag pool smartly with resto heavy attacks, a good rotation and regen from other bonuses, like racials or gear. If you're struggling as a healer to keep up your mag, being a vamp won't be enough to fix that--you need to rethink your build and rotation first.
Plus by being a non-vamp you can save those skill points for something else...