This is great reading, and great pictures from Pete! I am stunned to see those mile marks coming out that close, and you are using 1.001 factor as well! (Are you sure you didn't measure those for them at some point?)
I would definitely encourage folks who like to work in feet to get hold of a tape marked in tenths and hundredths of a foot. You can interpolate between hundredths to get a pretty good fix on thousandths.
Work in metric or imperial? I say bring 'em both on. I'll always use metric to determine final adjustments on a metric-length course, but in giving locations in U.S. I think giving distances in feet will have a better chance of being right, when some random person goes to find the point.
But using metric and standard works best when your calculator will hold a lot of items in memory so you can quickly pull up the sort of constant you want (mine is a Hewlett Packard with Reverse Polish Notation, but there are others).