This work measures the total economic impact, with a special focus on the agri-food sector of the Summer Jamboree, the largest international music festival of its kind taking place in a small town in central Italy mainly known for its beaches and seaside activities. The aim was to understand how and to what extent a large-scale event can bring benefits to the territory and the rural development of an area with a great, though only partially exploited, tourism potential. To this end, we used an Input-Output model fed by a sample survey carried out among the visitors and by the balance sheet data of the festival organizers. In order to obtain accurate and not overinflated estimated expenditures, we asked visitors to self-report their motivation for attending the area (seaside tourism vs festival), and then used their motivation as a weight to revise expenditures, thus providing a novel approach in impact assessment studies. The results show that the total economic impact reaches €28.8 million, triggered by a direct impact that, in the agro-industrial sector alone, amounts to €9 million. In addition, for 1€ public money invested in this event, 6.3€ is generated in the primary sector and in the food sector alone. Additionally, the estimated value of the sale of typical products amounts to €1.3 million. Hence, under certain conditions, major cultural events can bring significant benefits to the development of the territory, enhancing the whole agri-food value chain and favouring a more even distribution of the capital generated. This study is an important contribution to the literature, as it encourages the development of studies focusing on the specific spillovers of tourism, not necessarily rural, on the agricultural, rural and food sectors, that should interact more frequently with the economic system in general and with the touristic sector as well.