A recent report by GoBankingRates.com says that a low-income household earning $15,000 annually is worth about $74.78 to a bank — approximately $423.34 less per year than a household making $60,000. So it's no surprise that bankers aren't knocking each other down to get at this underserved market.

But despite the apparent profitability gap between bank customers and the unbanked, ignoring the latter could be a mistake, GBR found; an unbanked household could potentially pay more in fees than the more affluent customer's annual worth.

"The many financial needs of those who don't have a bank account [present] key opportunities that banks could be taking advantage of if they embraced the unbanked into their customer base more readily," the report said.

By doing so, FIs could claim fee-based services that are currently being transacted elsewhere, including:

• check cashing;
• money orders;
• wire transfers; and
• personal loans.

But, "beyond the numbers," GBR said, the unbanked offer an avenue into their local community that can be cultivated for future financial growth.

Read more about trends and statistics.