Most folks around here are more into lifting their JSW with Tiguan springs, could be some of the reason why you haven't seen a response. A lot of information can be found on the vortex, but most of it is opinion because things like tire pressure and bushing life need to be factored in.
If you notice your tires cupping, or see fluid leaking down the shock tube those are pretty reliable signs that it's time to replace. The bounce test still works, but you're looking for prolonged bouncing, meaning more than one up and down cycle. If the strut is working properly, not leaking fluid or cupping your tires it should absorb the bouncing motion quickly.
The price for the solo kit is attractive for sure, but for me personally I'd either go with eibach/H7R lowering springs (1.5" drop) and some Koni yellows (also adjustable) because I've had success in the past with hot wagons on the same set up (and put good cross country mileage on to boot), or just go AirLift be done with it and never feel a bridge joint or road seam again.
Looking forward to what you end up deciding.
