Yeah, it certainly adds a layer of depth - I'm fairly sure Sirius and Remus are not thinking of Lily at all, and neither is her name mentioned anywhere. Cleverly done on Rowling's part to realize she had to have Snape go around the bend here despite the lack of any reason why, at that point.

Which can't help with Snape's resentment afterwards. Makes it almost understandable how he treats Harry later on.

Hehe.

I meant agree about the being wonderfully cool, actually. But since you mention it, it's one thing if "stupid things" entails risking your life, quite another if it entails killing someone else. Killing Peter wouldn't have made them evil perhaps - though Rowling suggests later that it actually might have - but certainly it's not much of an expression if integrity.

I have to disagree again. Strongly, in fact. Neville is not particularly popular from the start, and yes, Harry isn't really much nicer to him than people in general (or at least not always). But Harry doesn't have any supposed friends who spend their time fawning over him the way we see Peter do over Sirius and James in book five. It annoys him when Colin Creevey engages in hero worship, and it disgusts him to see how Peter acts to Sirius and James in Snape's memory - and how they act to him in return. Peter is not merely some well-meaning but not very competent person like Neville (at first), he's also a brown-noser who has never really belonged in the Marauders gang. I couldn't say for sure Sirius wouldn't die for him, but I don't think he would have. At the very least, if it had been James (or Remus) or Peter, Sirius would have forgotten all about Peter in a split second. But in any case, comparing him to Neville isn't justified, I think.