Walking around the rocky/hilly/mountainous terrain of Afghanistan you want to reduce carrying weight and keep a low, stable, very firm footing, rather than increase performance at a cost of considerable added instability.

The best thing the US military could do for soldiers in those circumstances over the next ~20 years, is reduce the enormous carrying weight they deal with now. Any sort of added foot instability (poor grip, too much boosted height, unnatural added spring force, wrong materials, too much cushion, etc) is very dangerous in a war zone.