If you are at the point where you've learned how everything on the camera works, then the simple answer is yes, it's worth the upgrade. The camera can only do so much though, and a lot of it has to do with how you take a photo. If you're still if-y about the inner workings of a DSLR and haven't mastered it yet, then it's
not worth it at this point. Your pictures will be just as bad/good with the more expensive camera. My advice is, don't upgrade until you've squeezed everything out of your current camera. Something like getting sharper pictures for example, can be fixed by using a tripod & a low ISO.
Low ISO+tripod=sharper pics.
Your lens line-up are just fine for the kind of stuff you probably shoot. A 17-55mm f/2.8 is a great lens, but not worth the pricetag for what you'll use it for. What makes it good is its ability to shoot in low light situtations and having 2.8 max aperture throughout the zoom range. It won't automatically make your pictures any better than the 18-55mm kit lens. If you're taking pics of mostly stationary objects, you probably couldn't tell either pics apart if shot correctly.