If you switch to a 5D you will probably see an improvement to image quality as well. The chip and processor in the 5D are one of the best Canon have made. One magazine editor, that I submit work too noticed the quality improvement over the 20D. They were happy with the 20D results,but the 5D made a difference.
Problem is it's going to start to get expensive. Cheap lenses are out of the question. Welcome to the world of "L" Glass. Good news though the EF lenses will still fit your 30D, if not alway the other way round.