I was in a similar situation... with a good investment in EFs lenses to boot (17-55 f/2.8 for life!). I went with a 7D... and while it wasn't a huge upgrade IQ wise over my XSi... everything else about it _IS_ a huge upgrade.
I shoot mainly outside (landscape) so the weather sealing is killer. The 3 user programmable settings are unbelievably useful... I'll never be able to own another camera without them. The thumbstick and thumbwheel are a HUGE step up over a Rebel (you mean I can move around the menus without taking my gloves off when it's -10 degrees?!?! Sweet!).
And then there is the AF. While I consider myself a "landscape photographer" because that's what I do for "art"... the majority of my shutter releases are actually my wife, my new puppy, and "vacation" photos ;-) The AF in the 7D is unreal. So versatile. I love being able to smack the AF select button and select an AF point / zone on the fly while I'm looking through the viewfinder and even switch AF modes on the fly while looking through the viewfinder by hitting Mf. It's become so natural to me that I do it without even thinking.
Then there is even more:
- Electronic level: killer feature for landscapes
- Have different AF points selected in landscape vs left portrait vs right portrait
- FPS (for that puppy! Look here: http://www.canonrumors.com/forum/index.php?topic=5320.0
- Instantaneous exposure bracketing with a delay and mirror lockup (put the 7D in live view mode with bracketing on and 2 second delay and you press the shutter release (or hit your remote), the camera waits two seconds then silently fires off 3 exposures... perfect for lanscape work).
- And more...
My point here though is not to try to tempt you into buying a 7D... it's that you should look at the _other_ things a camera does beyond MEGA-Pixels and ISO noise... and really think about how a different machine could help you capture better photos... or get out of the way so you can let your creativity go.
If you're looking for a "step up" from a Rebel... and all you do is go to a new Rebel I think you'll be disappointed. All you're going to do is compare the shots you take at the pixel level to your old camera and you'll come away thinking that you should have sunk that $700 into another lens instead...
Instead... think about upgrading the _features_ of your camera. The workflow impacts will make you happier than you think....