Anyway, I like having options, really. I've played healers in games that had a mix of both hour long buffs that were relatively weak, but were still desirable, especially when stacked with other class buffs. They also had stronger single/multi-target shields or buffs that were much shorter, but considerably stronger, and could help turn the tides of a fight. I think having a mix of these would work well. Hell, you could even do your aura idea in here.
Skill: Protective Aura - decreases physical and magic damage by 2% for nearby party members.
Skill: Protect/Shell - decrease physical/magic damage by 5% for 15 minutes. 30 second cooldown.
Skill: Mighty Guard - decrease physical/magic damage by 20% for 45 seconds. 5 minute cooldown.
There. All skills accounted for, you've got your maintenance, you've got your life-saving buffs, you've got your party aura, and you've got your added level of strategy. Obviously these are just rough-estimated percentages and cooldowns and such, but I think it shows what I'm trying to go for. I like to add options, not take them away.