The deterioration and subsequent maintenance strategies significantly affect equipment reliability and availability. Spares replacement and or reuse are critical and complement both preventive and corrective maintenance strategies, although sparse work on their influence on maintenance cost and availability has been done. A discrete event simulation model incorporating preventive (PM) and corrective (CM) maintenance actions on multiple critical equipment components are advanced to investigate the influence of reusing and replacing spares on equipment availability and maintenance cost. Spare replacement is modelled during PM using block policy (BRP) or the PM kit. The stochastic component deterioration is modelled following the Semi-Markov Decision Process, where the impact of the maintenance strategy changes the remaining useful life of the components. The proposed study is demonstrated through the use case of a thermal power plant, where components of the turbocharger, one of the critical subsystems, are modelled. The study shows that reusing significantly improves availability but does not reduce cost due to compromising component reliability. The use of the PM kit improves performance significantly compared to using BRP under PM. At the same time, an increase in the PM interval depicts an increase in the maintenance cost and availability. These findings have significant implications while understanding the dynamics of the various maintenance actions and further offering maintenance decision support to enhance the equipment availability and reduce the maintenance cost for critical equipment.