Devarim 10:18 describes God as one "Who performs judgment for the orphan and widow, and loves the stranger..." Intuitively, it seems from this verse that there is a distinction between the orphan and widow, who need support and protection - and the stranger, who needs "love".
This distinction seems to be at the core of Megillat Ruth. Contrary to appearances, I think Naomi and Ruth were relatively financially secure after their return. Naomi's family was well off, and Naomi had sold their plot of land and they were presumably living off the proceeds. Ruth does go out to earn some extra income, but there seems to be no urgency in her decision to do so.
Rather, the book's tension comes from a different question: whether and with whom Ruth will be able to marry. Naomi originally tells Ruth to return to Moav because Naomi has no sons left whom she could marry. When a number of weeks working in Boaz' field have not led to a "shidduch" for Ruth, Naomi takes the initiative in arranging the meeting which leads to their marriage. This is the conclusion of the story: Naomi is once again part of a family, and Ruth - despite coming from the hated Moavite people and having no social standing of her own - gets an appropriate husband. Ruth has been rewarded, not by being rescued from poverty, but by being rescued from loneliness.
The laws of tzedakah obligate us to protect the rights of the poor. It seems from Megillat Ruth that this obligation is not only financial. We are equally obligated to seek out lonely and isolated members of society and to make them feel valued and welcome. It as just as easy to ignore the emotionally poor as the financially poor, so the mitzvah to help them is equally important, and the reward for doing so equally great.