Personally, I think the 5D mkIII specs suit the needs of landscape photographers. Or, at the very least, it suits my needs as a landscape/nature photographer.
My reasoning is thus: I'm often shooting in the morning or evening (golden hour) in low light at an f-stop between f/8 and f/11 and quite often I'll be using various filters from polarizers to graduated ND filters. This means that in order to get decent shutter speed I generally have to crank the ISO up, but I want as clean an image as possible. So the 5D mkIII's improvement on the mkII's ISO will be a great help.
Here's a tip: get a tripod and shoot at ISO 100 more often.