Effects of system size, coupling strength, and noise on the vibrational resonance (VR) of globally-coupled bistable systems have been investigated. The power spectral amplifications obtained by the three methods all show that the VR exists over a wide range of parameter values. The increase in system size induces and enhances the VR, while the increase in noise intensity suppresses and eventually eliminates the VR. Both the stochastic resonance and the system size resonance can coexist with the VR in different parameter regions. This research has potential applications to the weak signal detection process in stochastic multi-body systems.