Amid innovation-driven high-quality development, SRDI firms are core to fixing China’s industrial chain weaknesses, with R&D defining their operation quality. Using 1,473 2025 A-share listed SRDI enterprises as samples, this paper adopts a quadratic nonlinear regression model to test R&D investment intensity’s impact on ROA. A significant U-shaped link exists: pre-inflection-point R&D suppresses performance through cost crowding-out, while post-inflection-point R&D boosts performance via innovation gains. It provides empirical evidence for rational corporate innovation resource allocation and targeted governmental innovation policies.