What gets me is what they changed Shae into. Shae 2.0 lacks the naivete, sweet disposition (however feigned), and corn-fed charm that makes book Shae fit into place in the plot. Bronn, the clansmen, & Shae combine together in the books as a connection to the more common side of Westeros. Tyrion is besieged day and night with the affairs of noble people, the vast majority of which have it out for him. He takes solace in the simplicity of Bronn's nature (Money + Survival). Timmett Son of Timmett, Chella, Shagga, and the like are steadfast in their loyalty and Tyrion is amused by their mundane and savage view of the world (AKA: This bothers you? Kill it dead.)
Book Shae fits right in to this idea of that which is commonplace as less threatening and therefore comforting to Tyrion. The other women he encounters are noble and if not outwardly hostile to him only speak to him to further their own ends. Shae is just the opposite of those threatening women. They put on airs, speak with elevated language, and come from powerful families. Shae is straightforward, crass, and is as common as a weed. It is this difference from his enemies that makes Shae someone Tyrion lets his guard down around. She is his one bastion of support in a city full of people who want to see him fall. He trusts her because he thinks that she is loyal and too stupid to plot against him.
Shae 2.0 is similar in many ways to the noble women that threaten Tyrion in King's Landing. She keeps secrets, carries herself proudly, puts on airs, and she has said flat out that she is not a commoner. I fail to see how Tyrion could ever come to trust and love her. She doesn't fit into the rest of the people that he surrounds himself with in King's Landing.
One last thing. A major theme during Shae's time in King's Landing is the fact that Tywin clearly states that she's not to go to court. Once ousted from the manse Tyrion kept her in, Shae is hidden as a chambermaid. A common girl, however pretty and at times insolent can fit in as a lady's maid. Mysterious, exotic Shae 2.0 will stick out like a rose in a field of dandelions. Lady Tanda isn't the brightest but I think even she would notice...
EDIT-After I posted I read Unnamed's post...therefore I'll ad that on all points.