If additional money is available, some useful digital collections might emerge as a result. The result of the small solution will be a coherent digital collection that can add to the extended services of that library and other libraries. If additional money is available, the digital collection can be expanded or linked to other collections. Sometimes the Federal government does it right. That is, a small solution should be beneficial on its own terms, regardless of later developments.
Sustainability is another mark.
Many small solutions begin as grant-funded projects, but the good ones always yield results that can be carried forward on the regular budget, if need be. Small solutions should have clarity. They should be defined in terms of specific problems and specific goals, and they should demonstrably achieve those goals. Extendibility may be a mark of the best small solutions, but there's nothing inherently wrong with a closed solution. But when it comes to small solutions, it's useful to learn to admit failure and move beyond failures.