And "cold seed"... is that used in Angel scenes too, you think? Or is it just Spike?

I don't know, honestly. The argument against the term 'cold seed' as I understand it is that vamps are room temperature, not really cold. Although, I suppose that would depend on where the vamp was while they were doing the nasty. Spike's crypt was likely awfully cold, so I suppose that you could put forth a reasonable argument that there his seed would be cold. Although, if he'd just fed....

Hm. I think I'm frightened at how much thought I'm putting into vamp semen.