My mate paid for a sensor clean and calibration - cost him just over £100 but he reckons it was worth it. Like you he was not quite happy with the results and he got other folks to process his RAW pics and they were just a bit off. He then borrowed some L glass and did some tests which confirmed it was slightly off.
It sounds to me like the majority of your problem is in the post processing area. I used to spend ages on each pic until my mate showed me how to process a RAW image in under 2 minutes.
You have a reasonable lens on a cracking camera. I used to have a Sony Alpha A100 and Bigma (Sigma 50-500mm) and the results I got from them were more than adequate. They had their limitations and if I wanted to shoot in the same grim conditions as everybody else, then I expected poorer results. When I converted over to the 40D and 100-400 lens I expected my shots to improve in leaps and bounds - not so. I'm still getting to grips with the equipment but experimenting more.
I shoot Tv for fast jets. 1/640th at least at F8 if I can manage it and up the ISO to compensate. Don't be frightened of ISO400 and try and stick to the native ISO's like 100, 200, 400 etc without any exposure compensation. Any ISO in between is the result of software adjustment as is the exposure compensation. I shoot Av for helicopters and slow prop jobs - 1/125th or below again at F8 but you'll find you can come down the ISO if you don't want to be hitting apertures of F22 or above
Keep at it and it'll come
Al
