I have a few questions regarding the cleric's ability to spontaneously cast healing spells if they are good/neutral or injury spells if they are evil.

First, I notice that for the prepared, equivalent-level heal or injury spells, there's a significant penalty to their efficaciousness. Can anyone explain the details about that penalty?

Secondly, what's the deal with the injury spells? Yes, I get that lore-wise, they are negative energy equivalent of the heal spells. But are they really any good in combat, and is the ability to cast them spontaneously nearly as good as the ability to spontaneously heal?

My cleric almost never memorizes heal spells: she always spontaneously casts. I've not noticed a difference, though. The result is purely random, no matter how the spell is cast.

As for inflict spells, I don't think they're nearly as useful. If you're playing an evil party, it's your only choice, but if your cleric isn't evil, go for healing. To properly use the inflict spells, your cleric has to land a melee attack against the target, which means your cleric will have to wade into combat, which isn't always a good option if your cleric isn't built for it.