This is why a lot of times its better to not get the highest price dSLR body. Spend the money on the glass. The technology in the lens really isn't going to change, except for maybe the VR/IS lenses, but the glass itself isn't going to get better. A $1700 lens today will hold its value much better than a $1200 body will over time.
When I wrote my review for my D50 on
amazon I wrote at the end that considering the price and performance, your better off with the D50 over the D70s, save the (at the time) $300 and put that money towards better lenses. I don't know a whole lot about the Canon line, but it pretty much holds true. Their lenses will far outlive their bodies.