I'd say plan your budget so that you can spend on lenses at a
minimum, as much as you plan to spend on the body
. Until you can reach that point there's no sense in going for the more expensive body.
The D80 is a prefectly good body, sure the D90 has its advantages, but, at least in my mind, unless you already own some very good lenses, you'll get a better return for your money if you spend the extra 300 on lenses than on the better body.
Here's what glass I would make sure I have before upgrading a body:
Nikkor 35mm f/2.0
Nikkor 18-55/70/135/200mm VR zoom lens
Superwide angle zoom:
- Nikon
12-24mm f/4, or
- Sigma 10-20mm f/4-5.6
If you're into tele angles (I am not..) also
-
Nikon 70-200 f/2.8 VR
It's a matter of taste, but as I said... I own a D70 and don't plan to upgrade it before I spend $1~2K on lenses that I really want.
Of course many good lenses are worthless unless you're set up to have them ready when you need them (e.g. if you are travelling a lot, and cant or don't want to carry all that gear with you). If this is the case, than getting just one good all-around lens and the more expensive body would make more sense.