Ok as someone's who done cocaine a few times here's my thoughts:
1) It's possible the hooker (unless M and W were into cuckholding, W must have been a pro) wasn't just snorting the blow and was doing gummies where you rub the coke into the gums and it goes into the blood stream that way. Then maybe when they were kissing Barber ingested some.
2) I don't know why someone would want to do coke the night before an athletic event, especially one that requires lots of focus. The day after a night of coke I usually feel drained, tired and even depressed with the serotonin in the brain being down from a night of partying. I can't imagine having to vault with a coke hangover.
3) vaulting on coke definitely would be performance enhancing. You have no filter, the reptile comes out and you feel like you're the man on a coke high. I can definitely see it being a huge confidence boost for someone literally trying to throw themselves into the air.
4) nobody just wants to do a little bit of coke. it's kinda like pringles, once you pop, the fun don't stop.You buy a gram and keep snorting until it's gone. then maybe you hit the dealer back up for more. If M was a pimp, good chance he was W's dealer too.
5) i don't like coke. it's the most overrated/overpriced drug out there. the damage it does to the farmers and cultivating kids that produce is it is just as sad as the lives that are ruined by the people (market) addicted to the coke lifestyle and even worse, crack. a friend who dealt described it best calling it "fool's gold."