Maybe Bran in the show can finally become interesting now. Show-only people are baffled as to why I like his chapters so much in the books.
Yeah, they haven't done a terribly good job in the show demonstrating the power of a green seer. Aside from the Dragons and Others, Bran is the embodiment of the mysticism of this world, at least as it applies strictly to humans. I hope they start digging into his seeing and warging capabilities more this coming season, or else I fear they will be doing the character and the story's bigger picture a great disservice. As the strength of magic grows in general, I suspect it should playing a major role in the next two books. The show needs to reflect that so they don't paint themselves in a corner and have to retcon something. I'm surprised - I know GRRM is involved with the series, but I don't know why he didn't push for more mysticism in the Bran scenes, and they kind of glossed over how significant it was for him to warg into another human (Hodor).
I wonder if they will feature Coldhands in this season and, if so, will they bring back the actor who played Benjen Stark in S1?
I suspect they'll run into Coldhands, yes. IIRC, they don't get far beyond the wall before running into him.
As for Benjen, I don't think it's been confirmed that he really is Coldhands, but I think most people agree that it probably is. Throughout Bran's interactions with him, however, Bran does not recognize him as such - I think his face is always hidden by a cloak hood or something - so they could theoretically get anyone of similar build to play Coldhands until his reveal in later seasons, once it is determined who he really is.