Shape memory alloys are promising for vibration protection systems but their long-term performance is challenged by functional fatigue due to microplastic deformation. A previously developed microstructural model that explicitly accounts for the evolution of microplastic deformation is utilized in the research to investigate the influence of this phenomenon. A one-dimensional oscillatory system with a payload isolated by two TiNi alloy springs is investigated. Numerical simulations compare the device's response in austenitic and martensitic states, with and without microplasticity, under harmonic excitation. The results confirm that microplastic deformation significantly alters the dynamic characteristics of the system, highlighting the necessity of its inclusion for accurate performance prediction. Furthermore, the analysis demonstrates the superior performance of the shape memory alloy system compared to linear elastic counterparts, showing its inherent ability to mitigate resonance across a frequency range.