Replacing Power Cord On Flat Screen TV

Recently when repainting our family room I noticed that our Sony XRB TV had a replaceable power cord, so I connected an extra high end power cord to it to see what would happen. The cable that was included with the TV was surprisingly wimpy. To be honest I didn't really notice an improvement, but I'm not sure how to determine if improvements happened or not. Have any of you upgraded this cable on your high end TV and noticed improvements? If so, what should I be looking for to determine if it helped or not?

One thing I notice between playing Blu-Ray discs vs. a standard DVD in my upsampling DVD player is the clarity in the dark shadows of dark sections of movies. You can really notice the blotchiness of the transitions between dark and darker on the DVD vs the Blu-Ray. I've always attributed this to the quality of the media rather than any kind of power related issues, and in this example it is clearly demonstrated. Are there other things that clearly demonstrate the differences between power cables on hi-def TVs or am I just wasting time and money even bothering?

For reference, I am using a Monster Power Center to run my TV and other components through. I know Monster stuff is not true high end but I am not interested in buying a Shunyata or Richard Grey's unit for this purpose as I prefer to prioritize my audio system over video.