Increased Garrison Healing as a Civ Bonus?

I always liked the fact that Garrison Healing, even if it's pretty unless in anything but micro maps.

So in your guys' opinion; how good would garrison healing have to be to become useful for a civ? And if possible (cause I'm doubting if anyone would use it), what new Civ could this be a bonus for historically?

In case anyone is wondering, a tower heals about 6hp/minute/occupant, and a Castle heals a slightly better 12hp/minute/occupant.

So what are we thinking here? 300% faster? 600% faster? 1000% faster?! I'm excited to hear what people think!