I was in a similar situation to you a few years ago and I can tell you my experience if it helps.
I initially wanted to "get my feet wet" and really learn how to become a photographer. Almost any DSLR will allow you to do this. Understanding the interplay between ISO, aperture, shutter speed and how to use white balance, frame rates, etc etc to make a beautiful picture is something that DSLRs offer which *most* point and shoots don't, which really is the difference. Now, if you want to be technical, yes, the newer models will do many of these things better (better high ISO, faster frame rate, maybe allow 1/8000 instead of 1/4000 sec shutter speed) but these are really just technical details at the beginning. I truly appreciate now that a great picture can be taken with a point and shoot by a good photographer while a bad photographer can't make a good picture with the best DSLR now matter how hard they try. It's ALL about understanding you camera, lens, and light.
So, I bought an XSi to learn all this and now it is a little old for me and I want to upgrade to either a 5d Mark II or 7D. However, now I really do understand what aspects those cameras offer which my XSi doesn't, which, to be perfectly honest, most people do not when they buy a DSLR. There's really nothing sadder than using a DSLR in P or Green circle mode all the time sorry to say.
My advice: buy an XSi or similar, it really is a LOT of camera for the money, and if you get hooked, you can always upgrade.
One note: if you want video (which you may not think you do now, but really may when you're on vacation), get a TL series camera.