Daniel, I understand your angst! I started with an Olympus C4040, then it was an Olympus C5050. Then I got a Minolta A1. From there I bought a digital Rebel and then I had to have the 20D. Considering how long the 20D (while great for what it can do) will be 'current' and considering the high rate of turn over for dslr's, there is no way in h*e*double L that I would shell out the bucks neccesary for 1 series Canon.
On the flipside I have an old Graflex 22 that still works and that I still use. Also have a Horseman LE that I think I'd had run over with my VW to destroy; it'll also be with me for a long time.
Gosh, is there a point to all this rambling on? You betcha!
Get your medium format system - you will use it for years. If you have to sell your D70 to finance it, then go for it. It's not like you won't be able to buy another for pennies on the dollar in a few months. If you can keep the D70 then by all means, do so.
The important thing is that you keep shooting. After all, it's not the camera but you that supplies the creative force behind the lens. And if some digital measurebator tells you you're insane and that you won't be able to get film for *insert camera model here* then tell them to go pound salt. Then you could politely suggest that they seek professional help for their irrational fear of film.
Have fun with whatever you pick up

Edit: Just thought I should add that there is nothing wrong with digital capture. I guess I might have come off as harsh because I just hate it when someone bashes someone else's gear.