Interesting research suggests just giving the homeless money rather than advice or other forms of support, might be more effective. Also looks at other examples where social issues are treated by offering money. Would be interested in the nuances because "Punished by Rewards" has a lot of evidence of the downsides to financial incentives in many contexts. Though the homeless case doesn't really fit the "incentive" frame, some of the other egs in this piece do.
Reflections on the power of rehearsal, from a master performer