Probably get the most benefit from spinach the same way you do wheat grass which is through juicing it. Certain plants are very hard to digest. If you ever eaten a rather large spinach salad, the following day you dump a rather large spinach salad. If you juice it you get out all the good properties and leave behind the virtually impenetrable cell walls.
There is a juice bar near me that does all sorts of dark greens like spinach, parsley, wheat grass, among other things and i literally feel like a million bucks after drinking some of their stuff.