I already own the 2009 Blu-ray (with UK cut of the film). I was planning to get the 2013 10th Anniversary (US cut) but now I'm not going to spend the $10. Reason:
I went through the screenshots of the respective reviews for each version on Blu-ray.com. I found a few screenshots that were of the same scene for each version. They aren't exact matches to the specific frame, but three of them are really close (one of them is VERY close). So, I grabbed the images and threw them into Screenshot Comparison here:http://screenshotcomparison.com/comparison/44567/picture:0
No mouse on the image = 2009 version
Mouse on the image = 2013 version
I find that the 2009 version has an ever-so-slight edge in contrast. The 2013 image is a bit brighter, which results in a very small loss of contrast. That, alone, wouldn't cause me to stay away from the 2013 version.
I also find that the 2009 version also has an ever-so-slight edge in sharpness. In that first screen shot comparison (Liam Neeson's character Daniel with his stepson Sam, played by Thomas Sangster), look carefully at the white thread stitching near the neck on Sam's green shirt. The 2009 version is slightly sharper. You can also see the extra bit of sharpness in the white line on the pillow in the foreground.
It's my opinion that a bit more edge enhancement has been applied to the 2013 version, resulting in an increase in unnatural looking noise. What looks like film grain in the 2009 version, looks just a slight bit more like artificial manipulation in the 2013 version. The grain/noise seems more coarse in the 2013 version. One good place to see this is in screen shot #5. Look at the person's jacket standing near the window in the background. There's a diagonal line down the back (drab green on the left, dark green on the right). As you move the mouse back and forth over the image, notice how that line (and surrounding area) becomes more diffuse and appears to have larger grain in the 2013 version screen shot.
Obviously, in-motion, these differences would be far less noticeable (if noticeable at all). If I didn't own either one, I wouldn't be worried about buying the 10th Anniversary edition because, in my opinion, it certainly doesn't suck. But, based on my little comparison of screenshots, I prefer the look of the 2009 version. I'll take the very slight edge in sharpness, better contrast, and more film-like grain structure.
Since I already own the 2009 version, it seems silly to buy the 2013 version simply for a couple of song differences. Particularly since I've never seen the US cut. My first exposure to this film is the 2009 UK cut on Blu-ray. I'll stick with that.