Not only "improve their chances of success" but in many cases hit the jackpot. For many doping has been a game changer - these are the athletes who respond very well to PEDs. If they're good they become great...if they're great they become superhuman. Case in point with a few athletes: Marion Jones, everybody's sweetheart when she came out of college, won five freaking gold medals at Sydney (I believe that's a record). She was America's golden girl - the best of the best. Then came the drug bust with her involvement in BALCO using undetectable steroids ("The Clear") and even EPO as part of her cocktail of PEDs.
Then we have the heir apparent to El G, the great Moroccan miler in Rashid Ramzi. Double gold at Helsinki and the prestigious gold medal at Beijing. Though he "officially" ran for Bahrain he was a Moroccan, and the country of Morocco went crazy as they had a new hero to tout who kept the momentum going from the El G dynasty. But a year after that glorious Olympic victory, Ramzi tested positive for the high-octane blood booster CERA and his Kingdom came crumbling down.
And the great Kenyan miler Kiprop with all his Olympic & WC medals, claims to the 3rd fastest 1500 man ever, and who once said dopers should go to jail was busted for EP0 in an OOC test that he couldn't fanagel his way out of. How many young Kenyans aspiring to be like him were devastated by this? Hundreds? Thousands?
Funny thing is that if none of aforementioned athletes were ever busted for doping, very few would have questioned their performances (and if you did you'd be strongly criticized by many...think rekrunner). And if they didn't get busted, all we would have ever heard is: great athletes, super talented, hard workers, dedicated, gifted, special, great coaches, great training system, and so on and so forth.
I say great, dedicated, focused dopers!