Lyman,
I think the generally accepted accuracy of the calibrated bicycle method is +-0.1%. I would use that number rather than the 3-inch number.
The 10-30 foot accuracy for the absolute position of a point is an often-referenced number that has almost nothing to do with the accuracy of GPS in measuring distance. The reason is that almost all of that 10-30 feet is systematic error; it is the same for every point recorded. If two points are offset from their true positions by exactly the same distance and direction, the distance between them is still the same. How do I know most of that 10-30 feet is systematic error? Because if even 3-4 feet of it is random error (different for every point) people would be seeing GPS distances that were in error by 10% or more. I would leave off the 10-30 foot number and just say that people see long values on their GPS because they don't run the SPR.
I think the other parts of your response are good.
There have been several forum threads on the use and accuracy of GPS. You can see them all by going to
Measurement Forum topics
and scrolling down to the GPS listings.