I've moved from these entry level DSLR's to more professional DSLR's such as the Nikon D300 which I have now. I only made the upgrade because I found it was easier to change the settings and a lot quicker which is what I needed for the type of things I shoot.
If you want my honest opinion: I don't think you will get a very noticable change in image quality when upgrading bodies. Get some decent lenses, trust me, you'll be surprised how much these can improve your photographs.
I really wouldn't upgrade bodies until you need to.
But out of everything, DO NOT buy a body knowing it's going to be temporary until you can afford something else. Believe me, I have lost £100's by doing this. And of course, you'll have to relearn how to use the camera too. I'd rather have one and stick to it and know how to use that camera to its full potential.
Hope this helps ^^,
Thanks
John.