I've just upgraded to a Canon 6D from a T4i. I sold off an old film scanner to finance the purchase of the camera itself so I'm only out for the cost of the 16-35 f2.8L lens which I could probably be re-coup by selling the T4i and my 2 lenses for it (17-55 f2.8 and 10-22).
I'm trying to decide if it's worthwhile to keep the T4i and just eat the cost of the lens. I'm a hobbyist although I've done a few family weddings so I don't need a backup camera but it might be nice for harsher environments (Although if it was harsh enough I'd either keep with my cell phone camera or Canon P&S if I didn't care about photo quality and if I did care about photo quality I'd probably want to take my best camera in... It's not like I'm going to take my T4i on a roller coaster regardless and I haven't been out of the US for decades...)
It's gonna be hard to say good-bye to the 17-55 though lotsa sentimental value with that one (on the other hand I could get the 24-70L a little quicker... )
Mainly, is there any reason to keep a cropped camera around now that I'm going FF? (I don't have the 6D yet thanks to FedEx' goofy shipping but that's another story...)
Sell the T4i and buy a T3i, and sell the 17-55...use the T3i for extra reach on telephoto lenses in good light. Or, you could just do whatever you want to do and ignore my advice!