I think what Darcy means when saying that Elizabeth's retrospections must be contented due to ignorance, is that Elizabeth has done nothing wrong, so she must be ignorant of feelings of pain caused by the memory of bad behaviour. He's saying that Elizabeth has nothing to feel guilty about.

As for the combination of generous and sweet-tempered, yet spoiled and selfish - I think Darcy was imbubed with the idea of noblesse oblige to servants and the poor, but not to those like the Bennets who were of the gentry but of lower rank than him. The social divide in Regency England was very real, and I think it's very noticeable that when Elizabeth defends herself to Lady Catherine in chapter 56 she says: "In marrying your nephew I should not consider myself as quitting that sphere. He is a gentleman; I am a gentleman's daughter: so far we are equal.", rather than saying that such considerations are irrelevant. JA strikes me at times as being prepared to break down all the distinctions of rank above herself, while accepting as perfectly natural all the distinctions of rank below her. Darcy could well draw from this that the very poor and servants dependent on the wages he paid deserved courtesy and kindness, while the Bennets and Lucases of this world, able to fend for themselves financially, deserved no such courtesy.