IIRC your D80 has the same sensor as the D200 that Tristan talks about and a great feature set. Its only drawback is the limited high ISO range and this is only a drawback in poor light.
Investing in glass is a better long term plan than regularly upgrading camera bodies but sensor technology has improved a lot since the D80.
The only FX lens you currently have is the 70-300VR and this is worth keeping. 18mm on DX gives equivalent field of view of a 27mm on FX so I'm guessing for landscapes you might occasionally want something wider than your 18-70.
You have to make the choice sooner or later to stick with DX format and invest in wider glass for it and eventually a new DX body or start planning a change to FX.
If you stay with DX there is quite a choice of wider DX zooms from Nikon (10-24, 12-24) and two excellent inexpensive 10-20 EX variants from Sigma as well as the Tokina option. You could also opt for the 16-85VR DX zoom for a slightly wider range with similar image quality and sell the 18-70.
If going FX then the D600 and 24-120 F4 VR would give you the equivalent of the 16-85VR DX if you want a single lens landscape and walkaround solution. It will also give more than twice as many pixels per image and a huge increase in ISO and dynamic range. A less expensive starter option in FX is the D600 with its 24-85mm kit lens . This lens will give at least equivalent sharpness and a slightly wider view than your current DX setup and it also overlaps nicely with your 70-300VR at the long end. Next FX acquisition would be a wider lens
I would first make the FX/DX decision. If staying DX then wider glass might give more fun than a new DX body. Going to FX will be a massive step up in image potential but requires both a new body and at least one new lens.