If you're looking at the D70, I'd compare it to the 10D rather than the dRebel. The featuresets are more compatible. At the moment, the D70 is vaporware, and the price of the 10D may very well come down when the D70 is actually for sale. You can also find a decent number of them for sale over at fredmiranda.com for $1100 or so.
The only thing you really need to consider with a digital body is the crop factor - on the digital Canons (well, rebel and 10D) it's 1.6. On the 1D it's 1.3. It's nice because it turns your "standard" lenses into teles, but makes any wide-angle kind of expensive. It's also nice because you're using the "best" part of the lens - the edges are getting cropped out. You're less prone to vingetting as a result, I believe.
I don't know there's a % or ratio for body/lenses $$$ spent. Just keep in mind, at least with digital, you'll probably change bodies in the next three years, but may very well be keeping the lenses.
Seriously, check out the forums on fredmiranda. Lots of digital discussion, both Canon and Nikon, and a good mix of pros and amateurs. A wealth of information.
Ahh..and even the CF card isn't simple. Speed of the card is somewhat a concern, but the current Canon dSLRs don't take advantage of write acceleration. But even then, some cards are faster than others in the 10D.
J