There may have been a very good chance of Spinel joining Bloodstone if he had approached her near the beginning and promised her a serene, isolated place with no strings attached.  As things stand it's unlikely that she will.  Spinel may not exactly be an all-loving good guy, but she's already been given too much of a chance to learn empathy for her new friends.  That, and I'm thinking I want to make the effects of being touched by Aqua's compassion a plot point for her.