You can't see Willow seeking out greater knowledge and understanding of her power, even at great personal risk? You've obviously got a very different view of her character than I do... (Although it wouldn't be just 'to get more power' so much as 'to be able to use her powers to help people without risking going evil again', I think.)

I think that it was Coven that could help her with knowledge and understanding of her power without risk. And if she turned to a dark sorceress, she was really desperate.

And it wasn't just a personal risk - looks like she inadvertently shared knowledge that endangered all slayers.

Willow is clever and she has a very painful experience with black magic. The way I see her, she wouldn't turn to Saga Vasuki unless the latter was her last hope.

But, of course, Joss may have something else in his sleeve... :)