Re Vancian casting:
The things that have always bothered me about 0-1-2-3e casting rules as written are not that the caster is limited in how many spells per day she can cast, but in both what those spells are (memorization) and having to guess ahead of time what spells will be needed (memorization ahead of time). The end result was you'd see a magic-user with 10 1st-level spells in her book only ever memorize one or two of them, over and over again. And how many times have you as DM watched an otherwise ready-to-rock party stop dead for the day because they got to a door that the Thief couldn't open and the bashers couldn't break...and the MU didn't memorize
Knock. Aaaaargh!
3e's Sorcerer class was a revelation (though it took me a while to realize it; at first I thought the class was a waste of paper as it seemed so similar to the Wizard) - the answer lay in spell selection flexibility. In my current 1e-based campaign I've now got all caster types working like Sorcerers - if it's in your book (or on your list, for Clerics) and you have a slot left for that level, you can cast it. So far the result is that while some spells still get cast far too often, I'm seeing lots of other spells get used that would otherwise never see the light of day. Remains to be seen if this'll end up horribly broken at higher levels; they're now about the 3rd-5th range and so far, so good.
Re alignments and mechanics:
I've always like one aspect of alignment mechanics: that an aligned weapon or item can sometimes bite those of the wrong alignment who try to pick it up. Otherwise, alignment isn't that big a deal in my games...unless you're a Paladin, Cleric, Necromancer, or Assassin. But I really like the point raised earlier - and I apologize for forgetting who raised it - that alignment discussions in the pub were *far* preferable to bragging about the latest greatest character build; they showed (and led to) greater buy-in to the game as a whole, more often than not. And if you didn't care, well, hey, you're in the pub and there's beer; what more do you need?
One thing to remember, for you history buffs, is that in original D+D there was *no* good-evil axis - the alignments were lawful-neutral-chaotic. Good and evil came in with 1e AD+D...and have since slowly taken over.
Re demons and devils:
I've always seen both these "races" as areas where I as DM can lob in absolutely anything I can dream up. Particularly demons. And as for having lots and lots of layers of the Abyss, that's actually quite handy: if I need a particularly whacked-out setting for some off-plane adventure I'm dreaming up, then ::
whoop:: down to some random otherwise-unused plane of the Abyss they go.
Lan-"'greedy' is a modifier that can go on the end of any alignment"-efan