A hundred plus years of (un)life experience would definitely make Angel and Spike as different from Xander as they are and would be from each other. Beyond that, other than becoming human, it's never actually been established exactly what the Shanshu actually is. If it's to become human once more, with the chance of starting a totally new life, who's to say but what all memories of their undead existence might be totally wiped from their memories, along with the associated feelings of guilt, shame, and regret for what the monsters did? Receiving the Shanshu could mean that the lucky vampire starts a new life with a totally blank slate, or with only the memory of their pre-vampire lives.
Of course, that's an extremely drastic scenario, but if there is one thing that remains absolutely consistent in the Buffyverse, it's that, just when you think that you have everything figured out, an evil little troll named Joss will slip a kink in the plow line somewhere, turning a potentially happy ending into just the prelude to the next apocalypse.
