I've stayed out of this, because it's gone far, far afield of the original question, but I might point out here that there is a very major difference between Angel's initially coming to grips with his soul, and Spike accepting his. Upon receiving his soul, arguably the one person closest to him, whose opinion would seem to matter most, Darla, had the reaction of, basically, "What have they done to my boy? You've been (figuratively) destroyed, you're no longer worthy to be my mate, get out!" and even when he was later conditionally accepted back into the group, he was criticized for his new habit of only feeding on murderers and rapists. Basically, he was never led to believe that he was anything but less than he ad formerly been.
On the other hand, once Buffy learned that Spike had acquired his soul, she was totally supportive of him, praising him for risking everything to become a better man. She believed in and supported him, even over the very vocal objections of her friends. Even after the First Evil began using him to kill, she stayed on her side and never stopped believing in him. To me, at least, it is completely logical that Spike would have a far easier time coming to grips with his newly acquired soul than Angel ever was. For that matter, I wouldn't consider it too far a stretch of the imagination to believe that Angel, himself, never actually fully came to grips with his ensouled status before meeting and interacting wit Buffy.
