Averaging the spot readings does take into account the actual subject brightness range----you should read the darkest area of the scene that you wish to retain texture/detail and then the lightest area and then set the meter halfway between those readings. Most that use a spot meter will base the exposure on "placing" the most important shadow area i.e., one stop minus the reading, two stops minus the reading, etc...Then, will read the important high value and see where it "falls" relative to your placement of the shadow area---development is then decided upon given where the high value falls on the gray scale. It's all basic Zone System stuff, there's plenty of info out there from which to learn from if you choose. Like Rick A. said though----if you find that you are satisfied with the final result with "averaging" the low and high values, then roll with it. If you find you like your shadow areas but are unhappy with how the high values are being rendered, then I would suggest some deeper learning and use that spot meter in a more ZS like fashion.