The camera itself is not much different but it has a full frame sensor which is like the holy grail in digital cameras.
I plan to sell my old one on Ebay... maybe... I do love it so! Not yet decided but will probably sell it. If I get the good camera I will sell it with a lens (as they aren't compatible), if I get the cheaper camera I will sell it body only.
My old one is a 20D. Not exactly entry level (well it's 4 years old so pricewise it is) but functionality wise it's more serious hobbyist/semi pro.
If you are interested I will look at how much they are worth. It's been loved and cherished like you can probably imagine though! And was serviced and cleaned on the inside a couple of years ago.
If only I could decide... DH says I can have whatever I want, greed makes me want the good one, speed makes me want the cheaper one as the 5d mark II hasn't even been released yet and no idea when it will be.