The sad thing is, that's a plot twist that could be incredibly interesting in the hands of a good writer who knows the character. :/

Though I find it hard to believe that Spike wouldn't notice, because hey, no more crushing guilt! Unless, of course, IDW thinks that Spike doesn't feel particularly bad in the first place. I can't imagine they'd go so far as to have him still feel bad without a soul, just not as bad, or feel bad for different reasons, which might actually be workable.