Darla Moore came from humble roots. She grew up in Lake City, S.C., an agricultural community with a population of 6,675. After college, she moved to New York, where she achieved tremendous success in finance. She was the first woman on the cover of Fortune magazine. And with Condoleezza Rice, the former secretary of state, she became one of the first two female members of Augusta National Golf Club.About 10 years ago, Ms. Moore began spending more time in Lake City, where her grandparents had farmed and her father, a school principal and coach, was a local leader. She attributed her success to her upbringing among a diverse group of people who worked primarily in agriculture.But it seemed that Lake City’s best days in the tobacco and cotton trade were behind it, and Ms. Moore was determined to fix it up. In the last decade, she said, she has given about $100 million to support the town.Many once-great towns and neighborhoods in America have lost their luster. But the challenges of turning around a community are complex and may deter many philanthropists. For one, the job calls for more effort than just giving money. Experts say the person leading the charge needs to be part of the community, or substantial change will be difficult to accomplish.