I think the best way of spending miles is to buy vouchers from the online DiscoveryMall: http://www.vitalityshop.co.za/c-1646-vouchers.aspx#&panel1-2
List of vouchers available:
iTunes voucher code
Sunglass hut
Babies R Us
Naartjie
Reggie’s
Toys R Us
Majors for Minors
Hirsch’s vouchers
Mangwanani African Day Spa
Health Spa vouchers
Camelot Spa
Yuppiechef Vouchers
Superga Vouchers
Bibo Vouchers
Tempur Vouchers
Cape Union Mart vouchers
@home Voucher
Stuttafords vouchers
Superga vouchers
Spilhaus Vouchers
Tempur Vouchers
Yuppiechef Vouchers
Cycle Lab vouchers
The Pro Shop vouchers
They can also be converted to Avios points and SAA Voyager miles
https://www.discovery.co.za/portal/individual/card-miles-partner-avios
https://www.discovery.co.za/portal/individual/card-miles-partner-saa
You can also spend your Discovery Miles online:
http://www.actiongear.co.za
http://www.activitar.com
https://www.bidorbuy.co.za
https://www.bigconcerts.co.za
http://www.caffeluxe.com
http://www.capeunionmart.co.za
http://www.daddysdeals.co.za
http://dischem.co.za
http://www.eterniti.co.za
http://www.flook.co.za
http://www.hirschs.co.za
http://www.hpshop.co.za
https://www.incredible.co.za
http://www.istoreonline.co.za
http://www.kulula.com/payment-options/discovery-miles
http://www.loot.co.za
http://www.lovetodogood.org.za
http://www.netperfume.co.za
http://www.netgifts.co.za
http://www.netflorist.co.za
http://www.onedayonly.co.za
http://www.sterkinekor.com
http://www.sportsmanswarehouse.co.za
http://superbalist.com
http://www.takealot.com
http://www.theproshop.co.za
http://www.volpes.co.za
http://www.wantitall.co.za
http://www.yuppiechef.co.za
See here for more info: https://www.discovery.co.za/portal/individual/card-miles-lo