At level 4 I would have thought you might opt for Amplified Healing over Vampiric Assault. Here's my reasoning:

At level 20 with Vampiric Assault, if you're standing at a target, you're going to be doing 212.5 dps. That equates to 31.875 healing per hit. The pro of this approach is that is doesn't cost mana to heal. The downside however is that you must be constantly hitting in order to even accumulate the dps mentioned. For me, I only ever pick Vampiric Assault if I'm building a more auto-attack focused build e.g. Angelic Might + Blade of Justice.

With Amplified Healing at level 20, even with just 5 stacks of regeneration master, you're looking at 34 regen per second. This is without mana consumption, and without the need to attack. This benefit extends even further when considering that any healing from allies is increased, the healing well / regen orbs will heal you for more. Not sure if it does, but it may even be the case that angelic absorption benefits from Amplified Healing, meaning the skill is again much more useful.

What do you think?

TL:DR Amplified Healing > Vampiric Assault in healing builds