There are fine wide angle DX optics so FX isn't necessary to get wide coverage. In addition to low noise / high ISO the larger sensor has an edge on dynamic range that would be useful for landscape shooters.
Frankly, I don't think FX at 12 megapixels is a significant benefit for landscape photography. At 24 megapixels, yes. But the noise and dynamic range benefits wouldn't be apparent with higher resolution.
There are disadvantages to the D700 compared to the D300 for landscape photography too. The extra weight and bulk of the camera and of the wide angle lenses you'd likely use is signficant if you're hiking to do your shooting. Nikon's 14-24mm lens is a likely landscape shooting candidate because of its excellent performance - however, it's not only large, heavy and expensive, it won't accept filters. And super wide angle lenses aren't what I use for landscape photography. In fact much of my landscape work is telephoto. For superwide high resolution I shoot panoramic tiles.
Low light high ISO would be of some value to me but most of the time I use a tripod and really high ISO isn't something I've been wishing for as a landscape shooting tool. I see high ISO performance as more of an action tool or for available light handheld photography, not landscape work in particular.