I think it's unavoidable that Spike gets a soul eventually because there comes the time when you're running out of excuses to not just "stake the bastard already". The alternative is to kill him off or he becomes an occasionally popping up villain like Dru (which is still getting old after time). I was trying to think of something which could satisfy Spike fans. I know it's still a repetition to Angel. Hmm, he could become human... no, we had that already with Darla and it would ridicule Angel's arc. Don't know, Spike's a hard nut. 😀
The answer is in your question. No, since she activated "Potential Slayers". They weren't ordinated people in the first place. And a unique ancient artefact was required for that. She could enhance a normal person temporary I guess; like she did with herself when she wanted to kill Andrew and Jonathan.
Makes sense, though the removal of the happiness clause is overdue, imo. Hey... could be a nice sub-plot in our Willow goes over to A&F scenario. Willow finds a way to get rid of it and it contributes to the Wangel friendship. 🙂
She would need millions of Orbs of Thesulas for that.
The activation spell worked with the Slayer lines as in connections. Vampires, as shown in the comics, have a connection to their sires. Willow maybe could pull something off when she works on the very first vampire (forgot his name, the Old One Dracula changed into because of the Vampyr Book in S10). I wouldn't like the development, though, since Angel (and Spike) would lose their uniqueness.
Where? Is it good?
Agreed.
Why should the Trio summon Vamp Willow? Since Spike is also the villain in S06, the Trio gets less screentime. Otherwise, it could get too cramped on the villain side.