There are certain runs I fish that require deep wading. Not because you have to wade out farther, but because there is no sand/gravel bar behind you, but trees/somewhat steep bank, and you must wade up to your mid thigh often times, sometimes almost to your waist depending on water levels, to get in position to spey cast to the fish that sit in this run.
The depth at which you wade is another variable that you must consider when spey casting (on top of length of line out, sink tip, floating, or full sinking, length of rod, style of line, and other variables that influence how you time your particular cast for a particular situation). To a point though, use your common sense always and don't put yourself in a situation you don't need to be in.