A good camera is nothing in the hands of a bad photographer. How about you start by having us see what kind of images your getting out of your current camera before you start spending money.
If your not using your camera to its absolute limit, then theres no reason to upgrade. If you find that for your kind of work you need to shoot at 5fps or more, under low light where high ISO noise must be at a minimum, and shutter speeds need to be lightning quick, then you may need a better body. Or maybe you shoot landscapes for a company and need 20mp+ as they will be blowing up the images to huge sizes (and get this, I know a guy who does that for a living, and those guys still shoot old school large format film, as it still reigns as king).
Don't mean to be a jerk or anything, but you shouldn't even be considering doing it professionally if you can't decide for yourself if you need an upgrade.
I remember the two times I've ever actually felt it necessary to upgrade, the first time from a Olympus c-2500l (get this, 2.3mp, 400ISO max with super grain, no interchangeable lens, etc) to a D70 (with a cracked top lcd, mind you). That thing was awesome, But I found that for a lot of my pics I would need even faster fps and higher ISO capability, not to mention a more rugged body, so the switch to d200 came soon after, and only because I got an absolute STEAL. now I have a d70 that I love, and you know what I've found? the camera is better then I am, hence no reason to upgrade.
glass though (lenses)... you can ALWAYS invest in good glass. start there.
To give you an idea... I don't know what these "professionals" are talking about, but I know a professional who havs sold pictures for 1,000 dollars or more, which were taken on cameras which cost around 150 dollars. Heck, that same. heck, that very same photographer owns a 5d Mk II, and he tells me its a great camera, but now that hes held that kind of power, and KNOWS how to use it, he is actually considering stepping back a model or two and spending the money saved on glass or flashes.
You don't need a tank to kill a bird.