I think the Spark-Lite is probably as durable as it needs to be. I have one in my Ritter kit and since I bought two kits- one to play with and one to keep for emergencies it has given me ample opportunity to evaluate it.
What I would be concerned with as far as the Sparklite is its ability to withstand temperature extremes. Plastic does get very brittle in extreme cold and if the little wheel got clogged with ice or snow I could see a catastrophic failure occuring.
However, I always carry a firesteel on a beaded chain around my neck in addition to matches in a waterproof case.
The main advantage of the Sparklite to me is its ability to work one-handed. For the eventuality of being injured and needing to start a fire one-handed, it should have an adequate life-span.
If I lived in Alaska or elsewhere that temperatures plunged deeply, I'd probably explore the added durability of a metallic Sparklite type device. But a Bic lighter is pretty cheap in comparison...