Best strategy seems to be spending it on items that you can't use coupons on anyway (brands like Nike, electronics, etc...), as they would take the value of the Kohl's Cash off your total before applying any % off coupon.
For that reason, Kohl's Cash seems to have about an 80% resale value on eBay and elsewhere, because you can't use coupons like today's 20% off on the part of your total the Kohl's Cash pays for.