Jeff,
There are more theories on the meaning of the Departure Rule then there are about who killed JFK. While theories abound, pertinent quotes are rare.
One of the reasons that you don't see quotes, is that there is no specific requirement (or binding requirement) in USPAP calling for the development one, two or three approaches on every or any property type The standards are not, and cannot, be that speciic. USPAP requires that the scope of work not omit something that causes the results to be less than credible given the intended use of the appraisal. If you leave something out that might APPEAR to be applicable, you need sound reasons to support that. (For some of us the historical disrepute of the Cost Approach as a method of finding market value is a sufficently sound reason by itself)
Jeff, if you feel that your sales comparison approach does not get the job done, then maybe you have a situation where something else is applicable (althought that is hard to imagine). Just remember, a 2055 is a report form (SR 2), not an appraisal (SR 1). Anything that you consider to be necessary can be added. No form, in and of itself, 2055 or narrative, is by defition, a limited or complete appraisal.