I think there's a point where the party will have "enough" mitigation, damage and healing to clear all content (e.g. clearing content with the party's average iLevel being 80). I think beyond whatever "enough" is becomes preference.

I'm a fan of Mind and Piety. And I prefer Crit over Spell Speed and either over Determination if of same iLV.

Crit because it can lead to saving on MP IF the amount of healing was needed, which falls in line with my Piety preference (e.g. no Garuda i90 ring). In Cleric's Stance, the extra crit rate usually works out for me in overgeared dungeons.

I think of Spell Speed more as, how quickly can I finish a cast after dodging / repositioning / finish dropping the gamepad? The added side effect is that Medica II, Stoneskin and a non-Swiftcast "oh crap" Raise get to see some benefit.