This paper considers the challenges of increasing the effectiveness of a scenario approach to planning and management processes in the development of socio-economic systems under uncertainty. Methods are proposed to assess the effectiveness of scenario management based on encoding and comparing scenarios with a target scenario. For comparison, scenarios are formally represented, using a special algorithm, as a sequence of unique event identifiers. The assessment methods involve the event similarity of scenarios, the similarity of scenarios considering operations over a sequence of events, and the similarity of events based on the qualitative behavior parameters of significant factors. An important feature of scenario management is that the goal is formulated as the final state of the system and, moreover, as a sequence of events constituting the target scenario. The effectiveness of management options and the related scenarios is assessed using a target scenario (benchmark): the results of scenario modeling and the corresponding management options are compared with the benchmark. Scenario analysis is intended to support the management process of an event leading to the goal; therefore, it is reasonable to use as a benchmark the most rational scenario in terms of several characteristics with target values for the event being conducted. Scenario events are encoded using the scenario-event approach developed previously. This approach makes the transition from a real vector space (reflecting changes in the factor values of a scenario simulation model) to an event space. Practical examples are provided: the novel approaches to assessing the effectiveness of scenarios are used in several applied problems of ensuring the sustainable and safe development of complex socio-economic systems.