Right my views on this:
First off what controls an image you get?
Well first of its the photographer - he/she has to see the sight, frame the shot, set the settings (even if its to set auto mode) and fire the shutter.
Second off there is the lens - the lens directly affects the light quality entering into the camera body - as well as defining how you can frame the shot.
Third you have your camera body - its the recording device - it won't get a good shot if the first two options are poor quality no matter if its a rebel or a 1DM3.
That is how I view things and so I am willing to put my money into glass (and learning) long before I think about upgrading my camera body. When I moved from a sigma 70-300mm to a canon 70-200mm f2,8 IS L lens the jump in quality of image was very noticable - similar the jump with my 150mm macro which also let me get 1:1 macro images - something that before was impossible for me to get with my current glass and no matter what camera I had I still would not have been able to get those shots.
Better camera bodies do offer improved features - they will have lower noise at higher ISOs, faster shutter speeds, brighter viewfinders, faster and better AF, more settings custom functions, video mode (for some

) and many other things. They are well worth upgrading to, but if you only have poor glass you will still only get poor results (infact results can be worse since the camera will pick up all the imperfections of the glass as well!)
If you have your glass that you need at a high quality then I would consider upgrading your body - only upgrade your body eariler if your current one has a lack of a feature that you despiratly need to be able to make use of (such as AF motors for lenses which the lower end nikon entry DSLRs don't have)