D70 basically becomes a D70s with a firmware upgrade. Only real difference is D70s has a slightly larger LCD (2.00" vs 1.80").
D50 seems nice for the money. But personally the D70/s is a much better camera. Better kit lens, more features, faster, larger (fits my hands better), similar layout of controls of Nikons film cameras (especially having two control dials instead of one like the D50). I like have the ability to change many of the settings without having to use the menu.
Anyway, this is my opinion. You need to hold the camera and play with it before spending this kinda money.
K