I know this is an old post but I am a newby and was browsing the site. The question of docks is a common one here as well; usually treated as a useless weed. There are a number or Rumex species grouped as "dock" and each has its niche - from dryer sandy ground to swamps and bogs.
First point; food is needed to keep you warm and vertical - if it tastes good it is a bonus.
As already discussed, the plant (roots, leaves & seeds) can be eaten but (flavour aside) the energy acquired is not balanced by the energy required to process - overall a net nutritional loss on its own. On the positive side, most docks are deep rooted which means they are accessing water and nutrients below the root zones of our more palatable vegies. These nutrients are then lodged in the above ground portions and subsequently made available (recycled) as the top growth dies - great for harvesting and putting in the compost along with the nettles. Historically dock roots were used as a source of minerals (particularly iron) in the diet - I guess they didn't know why it worked, just that it did.
The deep root also penetrates and breaks up sub-soils, allowing water and surface nutrients to move down and enliven the subsoil.
So, if you can tolerate it in your fallow, don't allow it to seed and get the top growth into the compost it does have its benefits. However, you can also get similar benefits from the long, white "Japanese" radishes.
There are not more than five primary colours, yet in combination they produce more hues than can ever be seen - (Sun Tzu 600BC)