I think you make a good point about justices existing along a spectrum of adherence to methodologies, but I think some judges and justices also choose to avoid the main issue when the 'heuristics' are at odds with their principles. The most obvious example of a serial-parrier is the current chief.
Richard Posner is very upfront: he first decides, then finds rationale for that decision. Of course, the judge's role is to pick one decision among a range of possible decisions. As long as there is a section of public who supports that decision, all rationale judges provide make it appear non-arbitrary. This kind of explains why the same court ruled in opposing ways wrt segregation, etc.
