In this study, localized surface plasmon resonance (SPR) biosensors with gold nanowires regularly patterned on a gold film are considered for sensitivity enhancement. The theoretical investigation was conducted using rigorous coupled wave analysis (RCWA) in terms of various design metrics, such as the resonance angle shift, the SPR curve angular width (SPR CAW), and the minimum reflectance at resonance (MRR). Especially, when LSP modes couple resonantly, broad SPR CAW and shallow MRR as well as a large shift of the resonance angle can be observed due to absorptive damping and localized coupling. The results show that, in general, nanowires of a T-profile present more effective sensitivity enhancement than an inverse T-profile. The sensitivity enhancement mediated by the presence of nanowires has been clarified qualitatively based on the dispersion relation between metal film involving nanowires and surrounding dielectric medium. Moreover, optimal design parameters of nanowires are determined based on quantitative metrics that measure the sensor performance and the fabrication reliability.