Service monitoring is required for meeting regulatory requirements and verifying compliance to Service Level Agreements (SLAs). As such, monitoring is an essential part of web service-based systems. However, service monitoring comes with a cost, including an impact on the quality of monitored services and systems. To deliver the best value to a service provider, it is important to balance meeting monitoring requirements and reducing monitoring impacts. We introduce a novel approach to configuring the web service monitors deployed in a system so that they provide an adequate level of monitoring but with minimized quality impacts, delivering the best value proposition in terms of monitoring benefits and costs. We use a prototype system to demonstrate that by optimizing a web service monitoring system, we can reduce the impact of a set of deployed web service monitors by up to two thirds.