I have a D50 and I love it
I've used a D70 once or twice (the PR office where I work has one) and also love it.
I don't know what price point you're working under, or what the current price difference between the D70 and the D50 is... but you might consider the value of a D70 vs. D50 + extra lens.
Having said that the D70, aside from any feature differences, is probably more rugged than the D50, which may play into your choice based on your description.