As far as questing to level, you are correct in that you do not need a dedicated healer at all.
Either the shaman or the druid can be a very effective healer for your team.

If the shaman goes resto, you lose Totem of Wrath and Elemental Oath.
You can replace Totem of Wrath with Flametongue Totem, Earth Shield, Riptide, Mana Tide etc.

If the druid goes resto, you lose Moonkin Aura and Earth & Moon.
You gain Tree Aura and Wild Regrowth.

The druid as a DPS needs to worry about Eclipse procs and casting either Wrath or Starfire.
So it might be easier if the druid is the healer.
I personally love having a Resto Shaman in my group and would go with the shammy as the healer.
But if you do, the druid will either need two dps keys and to alternate between them based on the procs or to accept lower dps from maybe having your click macro cast/refresh Insect Swarm + Moonfire, and then randomly spam Wrath and Starfire.

As far as AoE goes, the druid can Hurricane either spec as the shammy can Magma Totem.
Hunter Volley and either Mage Arcane Explosion or Blizzard, with Consecrate... you'll be fine there.