Sarah,
I am conflicted some about the cis-playing-trans issue as well. I think it is more important for an actor to portray the role well. I think it may actually be better that a cis actor do the part, if done well, because that is an ally, who has made an effort to understand, in our fight presenting our case for us.
In the end, any well done depiction of our struggle and our normalcy is a good thing. Any depiction that caricatures us as sub-human in any way is to be boycotted, regardless of the actor.
Stevi