Personally, Joss' idea for bringing Tara back gave me shivers when I heard it. Then again, I am a complete and utter sap.
I think one of the differences between Buffy and Tara would be that Buffy sacrificed herself. As far as she was concerned, she was done. She'd been fighting the forces of darkness since the age of 15 and she was finally at peace. She was not only forcibly ripped away from that, but she woke up buried alive which just compounded the trauma. (Especially since if we go back to Nightmares in season 1, the Master does this to her, which puts it high on her list of fears considering the concept of the episode.)
Tara was killed by a stray bullet shortly after reconciling with her love. There's some unfinished business there. And I'd imagine Buffy would take pains to make sure Tara's arrival in the world of the living would be a little nicer than hers was.
Also, Buffy could easily have added an "if she is willing" clause to her wish.
As for why Tara and not Joyce or a life with Angel, by season 7 Buffy has come to grips with the loss of her mother. While she would love to her have her back, she's no longer hurting from the loss. Secondly, from a completely tactical perspective, facing off against the First Evil, Tara is more useful than Joyce. Tara not only can help them magically, but she could also help Willow with her confidence, which was still pretty shot magic-wise until the very end of the season.
As for a life with Angel, cookie-dough speech aside, Angel also has his own life right now. Wishing him away from that would be unfair.
As for wishes going wrong in the Buffyverse, our only evidence is has been those granted by Vengeance Demons, who are not the nicest of people by nature and have a good degree of leeway when granting a wish (see Anya turning the cheating boyfriend French when his disgruntled ex wished that he turn into a frog.) I'd imagine this wish would have been more stringless, or at least not actively vindictive.