By minor do you mean everyone who didn't appear in the main credits? In which case, despite the Seeing Red Trick, it would include Tara who was in quite a lot considering. And also Joyce, who like Tara was in it quite a lot- Joyce being the only character outside of the core four to appear in all seven seasons. So for those two, they were techincally minor characters under that description, but there's no point saying I wish to have seen more of them, because they were both in it a considerable amount.
Or do you mean minor as in only appeared in several episodes? So that would exclude those two mentioned above, but would include Jenny, Darla, Drusilla, Clem....
In which case, under THAT description, I felt Darla, Drusilla and Clem played just the right amount of their part in Buffy, but Jenny was kinda untapped Potential. That's not to say, I wish she had survived past Passion (Though it was incredibly tragic to have her go) but leading up to that episode I wish we had seen more of her. We only really got glimpses of her relationship with Giles and it would have been really nice to see much more of them together. Also, she was more an outside Scooby and beyond I Robot...You Jane, we never really see her actively helping and I would have liked to have seen her getting more involved in the Scooby action. Maybe some scrying, some Willow-esque computer mumbo-jumbo, maybe even stake one vampire, or helping Giles from getting knocked out or something. She just had a lot of potential I believe that went untapped.
