There was a hidden intent behind those questions that you touched upon with special abilities that affect multiple units.
The way I see it a unit should use an unmodified base value for its characteristic and then apply its own modifiers to that value. It just sits wrong with me to apply the same modifier TWICE, which is what you do if you replace the dependent base value (before modifiers) with the modified parent value and then apply the dependent model's modifiers.
That's a lot of fancy talk to get to the fact that if an Orc general (Ld 9) and a Goblin (Ld 6) are both subject to the Aura of Dark majesty, then the by first modifying the General's Ld you get Ld 8 that he can spread around, but then the Goblin gets Ld 7 when it to has to take into account the Aura. That adds up to a -2 penalty from an ability that only actually provides a -1 penalty.
Sure, that just means that you apply common sense and just add the condition that the dependent models don't apply modifiers from any source that has already been applied to the parent value. But what is the "same source"? If the Orc general and the Goblin were affected by two different Vampires each with the same Aura ability, how is that different from being affected by just one?
Again you apply common sense: The Aura would normally not apply multiple penalties to a unit within range of multiple Vampires, so we jusr make sure that the dependent models don't apply the same modifiers of the same TYPE of source that has already been applied to the parent value.
The same line of thought can bring you into the realm of characteristic modifying spells (both the Orc and the Night Goblin are subject to the same spell, or the same spell cast twice, once on each of the two) and different spells that affect the same characteristic.
It seems to me that common sense is both the boon and bane of this particular issue. It makes sense that a scared or disoriented general is less effective, that scared or disoriented troops are less effective then their unaffected counterparts, but that these two factors on combination need to be moderated... Somehow.
I think it's safe to assume that GW is going to make a half-assed attempt at addressing the issue that somehow makes it all worse.