if you will promise not to call me "sir" I'll promise to give you my best answer
Unless you specifically have plans for the second body - i.e. another purpose than just back-up - I suggest you save you wallet and buy whichever is least expensive on offer. After all, it's only supposed to back you up when your primary camera fails and hopefully that will not happen - it's a pretty unlikely occurrence.
Now, if you commanded $2,500 or more per shoot, it wouldn't be a problem to have two main cameras of semi-pro/pro grade. But if you were, you wouldn't be asking this question here
If the price--difference is minimal, the D70 and D80 has the built-in auto-focus motor. This means that you retain auto-focus with AF-D lenses. The D3000 require you to have AF-S lenses, which generally are more expensive (in some cases not, though). Speaking from experience, I can tell you that auto-focus is pretty neat to have for wedding shoots..lol. A spectacular and inexpensive all-round lens from Nikon is the 50mm F1.8 AF-D. It was introduced in 1986, but it still made from new today and it costs $120-130 from new. Although not a direct comparison, the 50mm AF-S costs $450 or so.
So this could make a D70/D80 a more attractive option, even from a economical perspective.
In respect of people with other opinions, I should tell you that there are those who believe that 6 mega-pixel isn't sufficient for large prints. While I maintain my opinion on the matter, it is of course correct that you cannot have max-resolution 300 DPI print of 6MP images for larger prints - however, I personally don't believe it makes any difference. Your monitor is 100 PPI, for example. But you have to make up your own mind. Personally I've gladly printed 18X12 inch images from a 6MP source-file, for example.
Good luck with the choice!