I refuse to believe that the Shanshu can't happen anymore. To me, it falls into the category of divine intervention, not magic (and definitely not the jurisdiction of W&H), so magic being gone from the Buffyverse won't interfere with its fulfillment at all. On a similar note, I also refuse to believe that signing a piece of paper, no matter what the piece of paper is or what kind of ink you're using, can have any bearing whatsoever on a prophecy. Real prophecies can't be thwarted, altered, or signed over like property. (And I disagree with Kean about the prophecy "the father will kill the son". Regardless of the fact that Angel did end up slitting Connor's throat, that prophecy was never real. That it came true anyway was an ironic coincidence. Prophecies can't be written on a whim.) To me, Angel's willingness to sacrifice what he views as the shining light at the end of his tunnel for the mission proves more than anything else that he's meant to receive it.
And I don't think that IWRY counts as the Shanshu, and the Gem of Amara certainly doesn't either. Those were a random fluke and an equally random MacGuffin, respectively, and it would have been incredibly anticlimactic and far too easy of a resolution if they hadn't been done away with. The Oracles tell us flat out that the Powers aren't the ones who granted his humanity in IWRY, it was just Mohra blood.
I don't think Spike ever had a shot at the Shanshu (nor will he ever have one), for several reasons:
1) The Oracles imply that, while the Mohra's blood turning Angel human was just random chance, he would be able to earn it from the Powers by saving mankind and averting the Apocalypse.
2) In "Blind Date", Angel is drawn to the Scroll of Aberjian before he even has any clue what it's about. This is an ancient prophecy, not a raffle prize or something anyone can be eligible for if they meet a couple of conditions. The outcome has been fixed since long before Liam and William were even born. It won't change just because both of them are vampires with souls as of 2002. Therefore, the vampire with a soul who was drawn to it without even knowing what it was in 2000 is still just as much the one to whom it refers from 2002 on as he always was.
3) W&H spends crazy amounts of resources on Angel, compared to the way they never so much as offer Spike a job or send someone to track him or assassinate him, a pattern which continues after he has a soul.
4) The destiny that gets written on Angel's chip in "The House Always Wins" (which takes place after Spike gets a soul), is described thus: "among other things, he's positioned to be a major player in the Apocalypse". Side note: I find it interesting that Angel is far more incapacitated when his free will is briefly removed in "Lineage" than when his destiny is removed in "The House Always Wins". It looks to me like the two are interdependent to a certain extent. He clearly needs both of them to be functional.
5) Eve and Lindsey artificially engineer everything that seems to support the idea of Spike being a candidate. I watched the episode again recently and was very careful to note that every single theory or suggestion that the chaos going on has something to do with Spike's destiny starts with either Eve or Sirk (who is working for her). None of it comes from a credible source.
I think the first one there is particularly important, because while the prophecy may not specify which side of the battle Angel will be on, the Oracles do right in the first season, and I trust them more than I trust the wording of an ancient piece of text that is susceptible to translation errors. Just because the text itself doesn't specify the details of the outcome, it doesn't mean they aren't already set, it just means they aren't already known by any of the characters (or W&H). W&H's efforts are not only wasted but are most likely counterproductive (much like Voldemort's efforts to kill Harry are counterproductive), even though they have the right ensouled vampire in their sights. In order to be rewarded with a pulse, Angel has to *save* mankind and *avert* the apocalypse, and it's prophesied that he will. (Also, as far as I'm concerned, he kind of did exactly that in season eight, though in the most unconventional way possible. If it is true that doing something different would have doomed the world, as Whistler said, then once the mass Slayer spell was cast, Angel only had one option if he wanted the world to survive. Which it did. Not that I'm happy with what he did, but if he really didn't have another option, then I won't hold it against him when I can simply hold it against the writers instead for putting him in such an impossible situation and pretend for my own peace of mind that S8 isn't the inevitable continuation of the TV series.)
Also, there's Angel's willing and determined attitude about helping the helpless, compared with Spike's typical snarky indifference and grudging helpfulness (unless Buffy's around, of course, in which case he miraculously manages to sprout nobler intentions). Furthermore, Spike doesn't even really want or care about the Shanshu. He "doesn't give a piss about atonement". But it's incredibly important to Angel. I don't believe he's accountable for anything Angelus did (and therefore he can't be forgiven for any of it--no more than one person can be forgiven for someone else's sins), but I do understand his desire to right those wrongs in whatever way he can, even if it doesn't repair the original damage, and his difficulty with absolving himself of crimes he didn't commit (because he remembers committing them--and, more importantly, that he *enjoyed* committing them). Being human would mean being rid of the demon part of him that actually is responsible for all those things. It would mean having the freedom to simply live his life without that awful burden. And it would mean having the freedom to experience happiness without fear that it's *too much* happiness. I don't understand how it's selfish to want something like that or to be striving towards that kind of goal. All it is, really, is having hope for a time when his existence won't be as blighted as it is now, and I won't hold that hope against him.
On the other hand, as far as we know, Spike doesn't the same happiness clause (it's never been tested, so we don't know for sure that his soul was restored free of exit clauses), he doesn't have the same difficulty with guilt, and he pretty much already does whatever he wants, so why should he get the Shanshu?
And then there's the matter of how Angel and Spike got their souls. I don't think that has anything to do with how good they are when they have them. In fact, I'd say that Angelus wanting nothing to do with his soul and trying to kill the people who want to restore it is a powerful testament to how much of a difference that soul makes, as are the measures Angel takes to ensure he keeps his soul, even though they make him miserable. He might have been cursed with it, but for the overwhelming majority of the time, he isn't trying to get rid of it. The more the human soul and the evil demon hate each other, the better it reflects on the soul, but the more it sucks to have both of them at once. So the fact that Spike's demon and William's soul can coexist more peacefully might make it easier to be him than it is to be Angel, but it doesn't mean he's a better person or that his soul is stronger.
Liam's soul and Angelus's demon clearly loathe each other, but they're fused together into Angel because of the curse, with the soul being what's in control of the mind and motor functions. (I'm not say that he'd go back to being the Liam of 1753 without the demon, because that's clearly not what happened when he was human in IWRY; as long as he has the memories of everything that's happened since then, for all intents and purposes he'll still be Angel, just without the vampiric physiology and urges.) But with Spike, fighting for his soul means his demon is kind of okay with it being there. Or, at least, it was okay with what he thought it would be like for it to be there, but he didn't really have a clue. I can't imagine that William's soul was terribly pleased with the situation, though. He didn't ask to get yanked out of whatever form of afterlife he was in and shoved back into that body any more than Liam's soul wanted to be shoved back into his body, so I feel like what soulless Spike did to William's soul by having it restored was just as cruel as what the Romani did to Liam's soul when they cursed Angelus. Still, it means that only one part of soulful Spike isn't happy about this. While Angel is at constant war with himself (but not in a schizophrenic way--I think of it as being more like extremely conflicting urges), Spike isn't quite so much. So Angel being cursed with his soul instead of fighting for it doesn't make him less good, it just makes him more tragic. And fighting to get a soul doesn't make soulful Spike more heroic, it just makes soulless Spike incredibly reckless and thoughtlessly cruel (but I wouldn't have expected any better of a soulless being). Angel fights for his soul every day. Spike gets off easy because he doesn't have to (as far as we know).
Oh! And the thing about Angel's curse and how the lack of magic may or may not be affecting it. To me, it seems most logical that it wasn't affected at all. The curse was cast using magic, but I don't see any evidence to suggest that it is sustained using magic or that the exit clause requires magic to work. Perfect happiness may be metaphorically magical, but it's not literally magic. So, even though it's a rather depressing theory, I think that he can still lose his soul through perfect happiness, but then that's it. No more soul for him. Ever. The silver lining there, I guess, is that perfect happiness looks like it'll be in pretty short supply for him from now on. Yay. The Shanshu can't come soon enough.
Wow, this ended up being waaaay longer than I planned...