The mulberry-dyke fishpond system represents China’s traditional circular agricultural heritage yet faces challenges of “circularity without economic viability” and preservation under modernization pressures. Taking the Globally Important Agricultural Heritage System site of Digang in Huzhou as a case study, this paper reveals fundamental shifts in its value structure through local research and interviews. Key findings include the following: (1) Significant decline in traditional economic value: Annual income from mulberry-dyke fishpond systems is extremely low, far below the per-mu yield of modern intensive aquaculture in the area. This has led to producer withdrawal and the disintegration of the base-pond structure. (2) Ecological and social values increasingly emerge and partially marketize: The system’s ecological service value is substantial and policy-recognized, with markets responding through a 100% premium on eco-fish prices. Concurrently, heritage-based cultural tourism integration generates significant new value—for instance, Digang village’s 2023 tourism revenue reached 140 million. However, these prominent non-market values still lack stable, adequate realization pathways. The core argument of this study is that the decline in mulberry-dyke fishpond systems stems from an imbalance in value structures rather than the disappearance of value. Their revitalization hinges on institutional innovation that transforms ecological and social value into sustainable market incentives. To this end, this paper proposes a systematic revitalization framework encompassing a concession system (incorporating community interest alignment and risk management clauses), regional brand certification, carbon sink value realization, and mechanisms for deep community participation. This approach aims to provide a Chinese solution for the sustainable development of similar agricultural cultural heritage sites, offering both theoretical insights and practical value.