You can't upscale a 960x540 file to 1080p and expect great quality. If that were the case...we wouldn't need better equipment for 2K, 4K, etc. In addition, how you manage the files in post processing, any compression applied, will greatly affect the outcome.
I read your example and tried an experiment. I recorded a 960x540 RAW, tranformed to DNG files, imported in Lightroom, applied color grading, and exported to 1920x1080p. Then used Quicktime Pro 7 to create the movie file. Went terrible. Pixels, looked like a bad VCR recording (if you are old enough to know what that is).
Suggestion: If you wan a "full screen look", you might try using one of the anamorphic aspect ratios (2.35:1, 2.67:1, etc). I used a 1280x320, and got continuos recording at 24fps. There is a trade off. The wider you go with your aspect ration, the shorter the height will be on your video. Wide look works for me, because when you export at the same aspect ratio your file was captured in, it will automatically look anamorphic when imported into your movie software (Premiere, FCPX, Avid, etc).
Bottom line: The 550d raw capabilities at this stage of the game are VERY limited. If you want more picture "real estate" (aka screen size), get a better camera. The 50D has a much better hardware, and you can get them used on Craigslist for about the same price as one of the Rebel cameras.
Cheers,
Yoda