The few tougher backs I have aren't slabbed. And probably won't be for a while since they're pretty much all in the 10-20 range. Maybe 30 on a good day.
I don't see much point in slabbing a worn creased card. The few nice ones I have eventually will be, primarily for the potential resale later on. I know what's what, and my wife knows a bit about cards. No telling wether my daughter will care at all yet. She does think cards are fun, but hasn't been kind to the few I've given her (Relax,they're mostly already creased 88 score
) The holders were more fun that the cards.....
Steve B