These are good points, Chris and I don't doubt your experience. Damping and mass of the wheel itself are certainly factors to consider. However, every single time I have encountered tail wheel shimmy on my plane and others, it was directly caused by (and solved by) adjusting the caster angle of the pivot axis. My plane was shimmying badly during my trip out west. The steel spring had sagged and was making for a negative caster angle. On that trip I purchased a used Grove aluminum spring. After installing the spring, all shimmy went away and as you can see, it has a positive caster angle. During the spring installation I disassembled the entire assembly to check for wear and anything else I could find. All was good and the swivel action is very free and loose. The chains also have some slack in them. No shimmy at all.
I would think the number of fold, unfolding cycles would have to be astronomical for there to be a problem. Like the elevator horn bolt on an Avid, this might be something to be inspected every so often if you fold on a regular basis.
I have that system shown in the box, installed on my plane now. I hope it lasts. My next step will be to replace the slip/sleeve joints on the muffler with proper ball and socket joints to allow for some movement. I believe this is the major problem area. It is where my first plane cracked (as well as around the stinger) and where my last system on the plane cracked prior to the stinger failure. If you look at the cracked muffler you can see the major reinforcement pieces around the slip joints. This misaligned the sleeves enough that assembling the system went from a real pain to almost impossible. IMO, this exhaust system is a poor design from Kitfox with many area that could be improved.