Dear Synomis, let me tell you about my recent experience, it might help. I myself is on a very tight budget and I do not earn a single cent from my photography. My interest in photography is very recent (just one year or so old). First I bought a canon G12 and started learning about photography. Soon I discovered that I needed "something more" to satisfy my growing expectations and ideas. But being on a tight budget I could only afford a second hand EOS 40D with a 50mm 1.8II (the lens was new of course). Yes it was a four year old camera, "only" 9 AF points, just 6.9 FPS, powered with a Digic III (I think), no video and no swivel screen. But 40D was the best I could do. I could have gone for EF-S 18-55 but I chose not to after reading about the image quality (in relative terms) vis-a-vis 50mm 1.8II. So I was happily snapping along and learning. Then a few months down the line I bought the EF 85mm 1.8. And now I had two, but both prime lenses. So I planned and started renting lenses from a local lens rental place. Coming to that later. Meanwhile, I went back home and met a friend of mine who had bought a EOS 50D with your exact lenses (18-55mm and 55-250mm). I was excited about EOS 50D and when I was buying my 40D I spent many hours drooling over 50D (microadjustment being one plus for it). I grabbed my friend's camera and started shooting photos. But I was not very happy with the images somehow. So I took out his 55-250mm lens and put it on my camera. I figured that I must not be able to handle his "better" camera because it was new to me. But when I snapped some more photos with his glasses on my camera (which I know how to handle) I was still not happy. Soon I understood it was not the camera but the lens (No disrespect to your or my friend's glasses). After being accustomed with my 50mm and 85mm I was, for something in the photos with those other lenses, not satisfied. Let's comeback to my lens rental story. Till now I have rented these lenses, EF-S 10-22mm, EF 100mm L2.8 macro, EF-S 17-55, EF 24-105. On my same 40D, I think (personal opinion) the EF 100mm L2.8 macro (used as a short/medium telephoto) gave me even sharper images than my EF 85mm. So what is the point of such a long story to reply to your question? My point I personally believe to make the investment in a camera body really worth it one needs to spend a lot on the glasses as well. Otherwise, as many have said, you can get better pictures with the same "mediocre" camera but with vastly superior lense. So my 2 cents will be with buying better glasses. At least if you have the opportunity, then rent out some very good glasses, mount them on you "old" camera and see if you see the difference or not. You can do the same thing with camera body as well, if you have that opportunity and can afford to spend that money for renting alone. See for yourself, but at least you will have your own judgement to back your decision. Last word, why buy 7D in 2012 if you want a "great" camera just for the sake of it? 7DII will probably come out soon. May be 70D. The body upgrade circle always goes on. Good and wonderful glasses not so much.
EOS 40D, EF 50mm 1.8II, EF 85mm 1.8, EF 22-55mm, some extension tubes