I have the same affinity for outsiders that I do for underdogs. I'm trying to decide whether one is an extension of the other or if I just identify with outsiders and therefore gravitate to them. Either way, I'm going to issue the warning that this post may not be the most balanced look at Tara. I like her too much.
Bringing a new or "replacement" character into an ensemble cast is rarely successful. Why should it be? Fans become invested in the interpersonal dynamics on a show as much as they do the lives of the individuals or the development of story arcs. It's impossible to introduce someone else without changing those dynamics to some degree.