I think there should be more Buffy goes back in time to fix things stories.  However you want to send her back as long as it is from post series.  Choices for her to be plopped back: Season 5 during Crush when Spike is declaring his love or during Fool for love when he tries to kiss her, Season 3 during Lover's Walk when they are at the magic box with Angel or even when she finds him at her house (before she lets Angel in the house)--remember according to cannon (and Dru) Spike was already in love with Buffy).  You can pick on Angel or Reily as much as you want but Buffy has learned her lesson and will put Spike first!!