Will the 6D actually be fine for us amateurs?

The 6D is fine for ANY photographer providing they have the skill to exploit it's full potential. The original 5D still takes fantasic photos, and check out the Iceland photo essay on the main page, where this photographer used a 5D Mark II, and the results are of course stunning.

Full frame is the way to go if you are primarily a landscape photographer. LOTS of great ultra wide angle lens choices, both zoom and fixed focal lengths (Canon of course, Zeiss...)