With a paladin, priest and warlock, you have a respectable level of buffing already. Aura, blessings, fort, COE and pet buffs. A totally mixed team could squeeze out more, but in your case you have to decide whether some 5-10% DPS increase or whatever is worth it to level more characters. Also, the three soulstones are a good way to give you that extra push on a tough boss to make up for your composition.

If you were running a PVE team of all shaman still, I would say it'd be worth rerolling a couple new characters. For you, it's totally your call.