Some groups, of course, would then get into arguments about what constitutes a life-threatening situation. (You know this to be true.

)
I think there needs to be a list of situations that automatically count (ie. any time someone is in combat and not surprised) and ones that automatically count as non-life-threatening (ie. a guard sitting at his post, bored, playing a card game) with the proviso "and the GM makes a ruling for any other situation". If the GM says someone is too on edge to be hit by the full effect, well, they're an NPC, their emotional state is something only he knows.
My personal preference, for sleep, would be that any situation where they know that falling asleep=death is definitely going to involve the combat effect. (This would mean that the elite guard, with their Overlord standing right behind them, can never be hit by the non-combat effect, because they're terrified already.)
So the other possible way of handling it is to have certain spells that can be cast one of two ways. They can either be cast as a standard action (or whatever D&DN's equivalent is), in which case, they have the multiple save thing going. Or they can be cast as "ritual magic," and require five minutes.
I think it depends on the spell which approach is superior. For self-buffs the ritual version is definitely best.
For sleep, I think the adrenaline version is best.
For SoD spells, I'd say the ritual would have to have a length measured in rounds for it to be worth it. It'd make for some very cool scenes with a 5 round ritual however, where the enemy is trying to get to the wizard and hit/grab/push them to disrupt the casting.
Hmmm, you could also have SoDs that have a huge range, if you have a piece of your opponents body (ie. hair, nail clippings, teeth) so that a longer version of the ritual can be done in secrecy from a mile away, but if you don't have such things the range is 30-50 feet, and you need line of sight.