You've got to figure out your wants / needs and go from there...
I recently went from the T1i to the 7d... my reasons for doing so were improved AF, faster AF, and better high ISO performance. The 7d delivered all of those and I'm very happy with the upgrade. A good side effect is that the bigger camera fits my gorilla hands much better. I'm just an enthusiast... no thought of ever taking it past here, and I really wasn't interested in full frame... for me,it came down to the fact that I knew after a while, I'd be looking to upgrade outside of the Rebel line, and if I went ahead and did it, I knew I'd get more for the T1i... if I had waited another 2 years or so until I actually outgrew the T1i, the resale on it would be depressingly low... by making the change now, it saved me money in the long run.
Canon 5dmkIII, Sigma 15mm f/2.8FE; 35mm f/1.4; Canon EF70-200 f/2.8L IS II; --- YN560 x 7
I'm not a professional photographer, and I don't want to be.
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