I am surprised you had issues with the 55-250 f/4-5.6. Most users actually call it the “nifty two-fifty” because its image quality is so good for the price. Mine actually got me some incredibly sharp (could see the barbules on a cardinal’s feather) images when shot with the lens’s strengths in mind. I also got a pretty nice quality kit lens with the T1i I got and have some good shots with it. I am a pixel peeper, so maybe one of the issues with the consumer quality lenses is that there is a lot more ‘room’ for what is considered a good copy and one can get an excellent, sharp copy and one can get a not so good copy as well.
I have to admit, also that the sharpness and image quality weren’t as consistent as they are with the higher priced lenses. My 70-200 f/2.8 IS II was shockingly sharp, even wide open – something that you can’t get with a lens you pay 90% less for. Then again, the 70-200 f/2.8 IS is 10 x the price, so once again it is easy to see why people are impressed with the 55-250’s performance.
(sudden aha! moment…) Wow. Maybe that is why I wonder how in the world all the fauxtogs are passing off these out of focus pictures as good work. Maybe part of it is a combination of lower-priced lenses and not knowing how to play to their strengths (i.e., shooting as much as possible in the sweet spot, etc.). It’s not that the images look badly focused as much as they are ‘slightly off’ or ‘muddy’ and fine detail like eyelashes, etc., are lost.
I have to admit to some confusion here (perhaps it is my bird brain?) – you say “alas, those nice lenses work even more seamlessly with my 5D Mark II.” Why is that a bad thing? Every lens I bought since focusing on creating work on a consistent basis that I was willing to sell to people will fit both an APS-C camera and full-frame, because I intend to add a full-frame camera to my lineup at some point. Is it a bad thing that the lenses work on both cameras? I have to admit a Rebel with a huge piece of glass on it feels kind of unbalanced in the hand and looks a bit awkward, but the best possible image quality comes from the best glass. That is the big factor. Also, lack of knowledge regarding the lens’s strengths when you are dealing with lower quality glass can often be a tripping point for less experienced photographers.
Once again, I would argue that you might see image quality improvement on your kit lenses if you take the UV filters off. I have noticed (pixel peeping again) visible differences on $2000 lenses between ‘nude’ and ‘covered.’ You are dealing with another layer of glass, its possible imperfections, its reflectance, etc., etc. These all can degrade image quality.
And please understand, I was using $100+ UV filters to cover the nice lenses. For some reason I don’t expect quite the same investment from whomever sold you the kit lenses. It would be a surprise to find a $100 UV filter on a $200-250 (depending on when you get it and what packages might be going on; some have even been able to get one new for $150) lens.